diff --git a/core/includes/form.inc b/core/includes/form.inc
index 17ca32c03f..f605920457 100644
--- a/core/includes/form.inc
+++ b/core/includes/form.inc
@@ -1036,17 +1036,13 @@ function _batch_populate_queue(&$batch, $set_id) {
 function _batch_queue($batch_set) {
   static $queues;
 
-  if (!isset($queues)) {
-    $queues = [];
-  }
+  $queues ??= [];
 
   if (isset($batch_set['queue'])) {
     $name = $batch_set['queue']['name'];
     $class = $batch_set['queue']['class'];
 
-    if (!isset($queues[$class][$name])) {
-      $queues[$class][$name] = new $class($name, \Drupal::database());
-    }
+    $queues[$class][$name] ??= new $class($name, \Drupal::database());
     return $queues[$class][$name];
   }
 }
diff --git a/core/includes/module.inc b/core/includes/module.inc
index 02a4f5d41f..bf0eae87de 100644
--- a/core/includes/module.inc
+++ b/core/includes/module.inc
@@ -41,9 +41,7 @@
  */
 function module_load_include($type, $module, $name = NULL) {
   @trigger_error("module_load_include() is deprecated in drupal:9.4.0 and is removed from drupal:11.0.0. Instead, you should use \Drupal::moduleHandler()->loadInclude(). Note that including code from uninstalled extensions is no longer supported. See https://www.drupal.org/node/2948698", E_USER_DEPRECATED);
-  if (!isset($name)) {
-    $name = $module;
-  }
+  $name ??= $module;
 
   if (\Drupal::hasService('extension.list.module')) {
     /** @var \Drupal\Core\Extension\ModuleExtensionList $module_list */
diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index ba8f4ee7b7..e2c59851b2 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -267,9 +267,7 @@ function theme_get_setting($setting_name, $theme = NULL) {
   $cache = &drupal_static(__FUNCTION__, []);
 
   // If no key is given, use the current theme if we can determine it.
-  if (!isset($theme)) {
-    $theme = \Drupal::theme()->getActiveTheme()->getName();
-  }
+  $theme ??= \Drupal::theme()->getActiveTheme()->getName();
 
   if (empty($cache[$theme])) {
     // Create a theme settings object.
@@ -1163,9 +1161,7 @@ function template_preprocess_container(&$variables) {
   // Special handling for form elements.
   if (isset($element['#array_parents'])) {
     // Assign an html ID.
-    if (!isset($element['#attributes']['id'])) {
-      $element['#attributes']['id'] = $element['#id'];
-    }
+    $element['#attributes']['id'] ??= $element['#id'];
     $variables['has_parent'] = TRUE;
   }
 
@@ -1226,9 +1222,7 @@ function template_preprocess(&$variables, $hook, $info) {
     $drupal_static_fast['default_variables'] = &drupal_static(__FUNCTION__);
   }
   $default_variables = &$drupal_static_fast['default_variables'];
-  if (!isset($default_variables)) {
-    $default_variables = _template_preprocess_default_variables();
-  }
+  $default_variables ??= _template_preprocess_default_variables();
   $variables += $default_variables;
 
   // When theming a render element, merge its #attributes into
@@ -1369,9 +1363,7 @@ function template_preprocess_page(&$variables) {
   $language_interface = \Drupal::languageManager()->getCurrentLanguage();
 
   foreach (\Drupal::theme()->getActiveTheme()->getRegions() as $region) {
-    if (!isset($variables['page'][$region])) {
-      $variables['page'][$region] = [];
-    }
+    $variables['page'][$region] ??= [];
   }
 
   $variables['base_path'] = base_path();
@@ -1568,9 +1560,7 @@ function template_preprocess_field(&$variables, $hook) {
   $variables['multiple'] = $element['#is_multiple'];
 
   static $default_attributes;
-  if (!isset($default_attributes)) {
-    $default_attributes = new Attribute();
-  }
+  $default_attributes ??= new Attribute();
 
   // Merge attributes when a single-value field has a hidden label.
   if ($element['#label_display'] == 'hidden' && !$variables['multiple'] && !empty($element['#items'][0]->_attributes)) {
diff --git a/core/includes/update.inc b/core/includes/update.inc
index ae13309396..1cbfb2477d 100644
--- a/core/includes/update.inc
+++ b/core/includes/update.inc
@@ -189,12 +189,8 @@ function update_do_one($module, $number, $dependency_map, &$context) {
     unset($context['sandbox']['#finished']);
   }
 
-  if (!isset($context['results'][$module])) {
-    $context['results'][$module] = [];
-  }
-  if (!isset($context['results'][$module][$number])) {
-    $context['results'][$module][$number] = [];
-  }
+  $context['results'][$module] ??= [];
+  $context['results'][$module][$number] ??= [];
   $context['results'][$module][$number] = array_merge($context['results'][$module][$number], $ret);
 
   if (!empty($ret['#abort'])) {
@@ -259,9 +255,7 @@ function update_invoke_post_update($function, &$context) {
     $context['finished'] = $context['sandbox']['#finished'];
     unset($context['sandbox']['#finished']);
   }
-  if (!isset($context['results'][$extension][$name])) {
-    $context['results'][$extension][$name] = [];
-  }
+  $context['results'][$extension][$name] ??= [];
   $context['results'][$extension][$name] = array_merge($context['results'][$extension][$name], $ret);
 
   if (!empty($ret['#abort'])) {
@@ -357,9 +351,7 @@ function update_get_update_list() {
           $replacements = ['', '$2', '', ''];
           $description = preg_replace($patterns, $replacements, $func->getDocComment());
           $ret[$module]['pending'][$update] = "$update - $description";
-          if (!isset($ret[$module]['start'])) {
-            $ret[$module]['start'] = $update;
-          }
+          $ret[$module]['start'] ??= $update;
         }
       }
       if (!isset($ret[$module]['start']) && isset($ret[$module]['pending'])) {
diff --git a/core/lib/Drupal/Component/Graph/Graph.php b/core/lib/Drupal/Component/Graph/Graph.php
index 6fe9cf21b0..cbd0511d5f 100644
--- a/core/lib/Drupal/Component/Graph/Graph.php
+++ b/core/lib/Drupal/Component/Graph/Graph.php
@@ -75,9 +75,7 @@ public function searchAndSort() {
 
     foreach ($state['last_visit_order'] as $vertex) {
       $component = $this->graph[$vertex]['component'];
-      if (!isset($component_weights[$component])) {
-        $component_weights[$component] = 0;
-      }
+      $component_weights[$component] ??= 0;
       $this->graph[$vertex]['weight'] = $component_weights[$component]--;
     }
 
@@ -100,9 +98,7 @@ public function searchAndSort() {
    */
   protected function depthFirstSearch(&$state, $start, &$component = NULL) {
     // Assign new component for each new vertex, i.e. when not called recursively.
-    if (!isset($component)) {
-      $component = $start;
-    }
+    $component ??= $start;
     // Nothing to do, if we already visited this vertex.
     if (isset($this->graph[$start]['paths'])) {
       return;
diff --git a/core/lib/Drupal/Component/Plugin/LazyPluginCollection.php b/core/lib/Drupal/Component/Plugin/LazyPluginCollection.php
index 6574c5b3da..db985a16d8 100644
--- a/core/lib/Drupal/Component/Plugin/LazyPluginCollection.php
+++ b/core/lib/Drupal/Component/Plugin/LazyPluginCollection.php
@@ -116,9 +116,7 @@ public function remove($instance_id) {
    *   (optional) The configuration used by this instance. Defaults to NULL.
    */
   public function addInstanceId($id, $configuration = NULL) {
-    if (!isset($this->instanceIds[$id])) {
-      $this->instanceIds[$id] = $id;
-    }
+    $this->instanceIds[$id] ??= $id;
   }
 
   /**
diff --git a/core/modules/big_pipe/tests/modules/big_pipe_test/src/BigPipeTestController.php b/core/modules/big_pipe/tests/modules/big_pipe_test/src/BigPipeTestController.php
index 8a0e9c9d9f..71427174f2 100644
--- a/core/modules/big_pipe/tests/modules/big_pipe_test/src/BigPipeTestController.php
+++ b/core/modules/big_pipe/tests/modules/big_pipe_test/src/BigPipeTestController.php
@@ -198,9 +198,7 @@ public static function counter() {
     // once with the same parameters.
     static $count;
 
-    if (!isset($count)) {
-      $count = 0;
-    }
+    $count ??= 0;
 
     $count++;
 
diff --git a/core/modules/block/src/Entity/Block.php b/core/modules/block/src/Entity/Block.php
index ece8de38ab..01b7428bb9 100644
--- a/core/modules/block/src/Entity/Block.php
+++ b/core/modules/block/src/Entity/Block.php
@@ -281,9 +281,7 @@ public function setVisibilityConfig($instance_id, array $configuration) {
    * {@inheritdoc}
    */
   public function getVisibilityConditions() {
-    if (!isset($this->visibilityCollection)) {
-      $this->visibilityCollection = new ConditionPluginCollection($this->conditionPluginManager(), $this->get('visibility'));
-    }
+    $this->visibilityCollection ??= new ConditionPluginCollection($this->conditionPluginManager(), $this->get('visibility'));
     return $this->visibilityCollection;
   }
 
@@ -301,9 +299,7 @@ public function getVisibilityCondition($instance_id) {
    *   The condition plugin manager.
    */
   protected function conditionPluginManager() {
-    if (!isset($this->conditionPluginManager)) {
-      $this->conditionPluginManager = \Drupal::service('plugin.manager.condition');
-    }
+    $this->conditionPluginManager ??= \Drupal::service('plugin.manager.condition');
     return $this->conditionPluginManager;
   }
 
diff --git a/core/modules/book/src/Form/BookOutlineForm.php b/core/modules/book/src/Form/BookOutlineForm.php
index 0bf60353ce..444c1d92bf 100644
--- a/core/modules/book/src/Form/BookOutlineForm.php
+++ b/core/modules/book/src/Form/BookOutlineForm.php
@@ -83,9 +83,7 @@ public function form(array $form, FormStateInterface $form_state) {
     }
 
     // Find the depth limit for the parent select.
-    if (!isset($this->entity->book['parent_depth_limit'])) {
-      $this->entity->book['parent_depth_limit'] = $this->bookManager->getParentDepthLimit($this->entity->book);
-    }
+    $this->entity->book['parent_depth_limit'] ??= $this->bookManager->getParentDepthLimit($this->entity->book);
     $form = $this->bookManager->addFormElements($form, $form_state, $this->entity, $this->currentUser(), FALSE);
 
     return $form;
diff --git a/core/modules/book/src/ProxyClass/BookManager.php b/core/modules/book/src/ProxyClass/BookManager.php
index 8ee2568989..dd297a45ca 100644
--- a/core/modules/book/src/ProxyClass/BookManager.php
+++ b/core/modules/book/src/ProxyClass/BookManager.php
@@ -60,9 +60,7 @@ public function __construct(\Symfony\Component\DependencyInjection\ContainerInte
          */
         protected function lazyLoadItself()
         {
-            if (!isset($this->service)) {
-                $this->service = $this->container->get($this->drupalProxyOriginalServiceId);
-            }
+              $this->service ??= $this->container->get($this->drupalProxyOriginalServiceId);
 
             return $this->service;
         }
diff --git a/core/modules/book/src/ProxyClass/BookUninstallValidator.php b/core/modules/book/src/ProxyClass/BookUninstallValidator.php
index 2ba59bf055..79a987309c 100644
--- a/core/modules/book/src/ProxyClass/BookUninstallValidator.php
+++ b/core/modules/book/src/ProxyClass/BookUninstallValidator.php
@@ -60,9 +60,7 @@ public function __construct(\Symfony\Component\DependencyInjection\ContainerInte
          */
         protected function lazyLoadItself()
         {
-            if (!isset($this->service)) {
-                $this->service = $this->container->get($this->drupalProxyOriginalServiceId);
-            }
+              $this->service ??= $this->container->get($this->drupalProxyOriginalServiceId);
 
             return $this->service;
         }
diff --git a/core/modules/breakpoint/src/BreakpointManager.php b/core/modules/breakpoint/src/BreakpointManager.php
index 070b0bf043..f339e3b5d5 100644
--- a/core/modules/breakpoint/src/BreakpointManager.php
+++ b/core/modules/breakpoint/src/BreakpointManager.php
@@ -167,9 +167,7 @@ public function getBreakpointsByGroup($group) {
 
     $instances = [];
     foreach ($this->breakpointsByGroup[$group] as $plugin_id => $definition) {
-      if (!isset($this->instances[$plugin_id])) {
-        $this->instances[$plugin_id] = $this->createInstance($plugin_id);
-      }
+      $this->instances[$plugin_id] ??= $this->createInstance($plugin_id);
       $instances[$plugin_id] = $this->instances[$plugin_id];
     }
     return $instances;
@@ -186,9 +184,7 @@ public function getGroups() {
     else {
       $groups = [];
       foreach ($this->getDefinitions() as $plugin_definition) {
-        if (!isset($groups[$plugin_definition['group']])) {
-          $groups[$plugin_definition['group']] = $plugin_definition['group'];
-        }
+        $groups[$plugin_definition['group']] ??= $plugin_definition['group'];
       }
       $this->cacheBackend->set($this->cacheKey . '::groups', $groups, Cache::PERMANENT, ['breakpoints']);
     }
diff --git a/core/modules/ckeditor5/ckeditor5.module b/core/modules/ckeditor5/ckeditor5.module
index 561795fa95..d319dd5d7e 100644
--- a/core/modules/ckeditor5/ckeditor5.module
+++ b/core/modules/ckeditor5/ckeditor5.module
@@ -600,9 +600,7 @@ function ckeditor5_config_schema_info_alter(&$definitions) {
  */
 function _ckeditor5_theme_css($theme = NULL): array {
   $css = [];
-  if (!isset($theme)) {
-    $theme = \Drupal::config('system.theme')->get('default');
-  }
+  $theme ??= \Drupal::config('system.theme')->get('default');
   if (isset($theme) && $theme_path = \Drupal::service('extension.list.theme')->getPath($theme)) {
     $info = \Drupal::service('extension.list.theme')->getExtensionInfo($theme);
     if (isset($info['ckeditor5-stylesheets']) && $info['ckeditor5-stylesheets'] !== FALSE) {
diff --git a/core/modules/comment/src/CommentManager.php b/core/modules/comment/src/CommentManager.php
index ba26943fe4..084cf84cd5 100644
--- a/core/modules/comment/src/CommentManager.php
+++ b/core/modules/comment/src/CommentManager.php
@@ -151,14 +151,12 @@ public function addBodyField($comment_type_id) {
    * {@inheritdoc}
    */
   public function forbiddenMessage(EntityInterface $entity, $field_name) {
-    if (!isset($this->authenticatedCanPostComments)) {
-      // We only output a link if we are certain that users will get the
-      // permission to post comments by logging in.
-      $this->authenticatedCanPostComments = $this->entityTypeManager
-        ->getStorage('user_role')
-        ->load(RoleInterface::AUTHENTICATED_ID)
-        ->hasPermission('post comments');
-    }
+    // We only output a link if we are certain that users will get the
+    // permission to post comments by logging in.
+    $this->authenticatedCanPostComments ??= $this->entityTypeManager
+      ->getStorage('user_role')
+      ->load(RoleInterface::AUTHENTICATED_ID)
+      ->hasPermission('post comments');
 
     if ($this->authenticatedCanPostComments) {
       // We cannot use the redirect.destination service here because these links
diff --git a/core/modules/comment/src/CommentStatistics.php b/core/modules/comment/src/CommentStatistics.php
index 5b38f4549e..16a5fd508d 100644
--- a/core/modules/comment/src/CommentStatistics.php
+++ b/core/modules/comment/src/CommentStatistics.php
@@ -124,11 +124,9 @@ public function create(FieldableEntityInterface $entity, $fields) {
       if ($entity instanceof EntityOwnerInterface) {
         $last_comment_uid = $entity->getOwnerId();
       }
-      if (!isset($last_comment_uid)) {
-        // Default to current user when entity does not implement
-        // EntityOwnerInterface or author is not set.
-        $last_comment_uid = $this->currentUser->id();
-      }
+      // Default to current user when entity does not implement
+      // EntityOwnerInterface or author is not set.
+      $last_comment_uid ??= $this->currentUser->id();
       // Default to REQUEST_TIME when entity does not have a changed property.
       $last_comment_timestamp = REQUEST_TIME;
       // @todo Make comment statistics language aware and add some tests. See
@@ -241,11 +239,9 @@ public function update(CommentInterface $comment) {
       if ($entity instanceof EntityOwnerInterface) {
         $last_comment_uid = $entity->getOwnerId();
       }
-      if (!isset($last_comment_uid)) {
-        // Default to current user when entity does not implement
-        // EntityOwnerInterface or author is not set.
-        $last_comment_uid = $this->currentUser->id();
-      }
+      // Default to current user when entity does not implement
+      // EntityOwnerInterface or author is not set.
+      $last_comment_uid ??= $this->currentUser->id();
       $this->database->update('comment_entity_statistics')
         ->fields([
           'cid' => 0,
diff --git a/core/modules/comment/src/CommentViewBuilder.php b/core/modules/comment/src/CommentViewBuilder.php
index 0e4e024dd5..235456a1ee 100644
--- a/core/modules/comment/src/CommentViewBuilder.php
+++ b/core/modules/comment/src/CommentViewBuilder.php
@@ -164,9 +164,7 @@ public function buildComponents(array &$build, array $entities, array $displays,
         ];
       }
 
-      if (!isset($build[$id]['#attached'])) {
-        $build[$id]['#attached'] = [];
-      }
+      $build[$id]['#attached'] ??= [];
       $build[$id]['#attached']['library'][] = 'comment/drupal.comment-by-viewer';
       if ($attach_history && $is_node) {
         $build[$id]['#attached']['library'][] = 'comment/drupal.comment-new-indicator';
diff --git a/core/modules/config/src/Controller/ConfigController.php b/core/modules/config/src/Controller/ConfigController.php
index 0c0f486865..f2375d05dc 100644
--- a/core/modules/config/src/Controller/ConfigController.php
+++ b/core/modules/config/src/Controller/ConfigController.php
@@ -171,9 +171,7 @@ public function downloadExport() {
    *   Table showing a two-way diff between the active and staged configuration.
    */
   public function diff($source_name, $target_name = NULL, $collection = NULL) {
-    if (!isset($collection)) {
-      $collection = StorageInterface::DEFAULT_COLLECTION;
-    }
+    $collection ??= StorageInterface::DEFAULT_COLLECTION;
     $syncStorage = $this->importTransformer->transform($this->syncStorage);
     $diff = $this->configManager->diff($this->targetStorage, $syncStorage, $source_name, $target_name, $collection);
     $this->diffFormatter->show_header = FALSE;
diff --git a/core/modules/content_translation/src/ContentTranslationHandler.php b/core/modules/content_translation/src/ContentTranslationHandler.php
index a4894b99f1..6b9ea93f9c 100644
--- a/core/modules/content_translation/src/ContentTranslationHandler.php
+++ b/core/modules/content_translation/src/ContentTranslationHandler.php
@@ -596,9 +596,7 @@ public function entityFormSharedElements($element, FormStateInterface $form_stat
 
     // @todo Find a more reliable way to determine if a form element concerns a
     //   multilingual value.
-    if (!isset($ignored_types)) {
-      $ignored_types = array_flip(['actions', 'value', 'hidden', 'vertical_tabs', 'token', 'details', 'link']);
-    }
+    $ignored_types ??= array_flip(['actions', 'value', 'hidden', 'vertical_tabs', 'token', 'details', 'link']);
 
     /** @var \Drupal\Core\Entity\ContentEntityForm $form_object */
     $form_object = $form_state->getFormObject();
diff --git a/core/modules/dblog/src/Plugin/views/filter/DblogTypes.php b/core/modules/dblog/src/Plugin/views/filter/DblogTypes.php
index ed8f547166..4e4d200c55 100644
--- a/core/modules/dblog/src/Plugin/views/filter/DblogTypes.php
+++ b/core/modules/dblog/src/Plugin/views/filter/DblogTypes.php
@@ -16,9 +16,7 @@ class DblogTypes extends InOperator {
    * {@inheritdoc}
    */
   public function getValueOptions() {
-    if (!isset($this->valueOptions)) {
-      $this->valueOptions = _dblog_get_message_types();
-    }
+    $this->valueOptions ??= _dblog_get_message_types();
     return $this->valueOptions;
   }
 
diff --git a/core/modules/field/src/ProxyClass/FieldUninstallValidator.php b/core/modules/field/src/ProxyClass/FieldUninstallValidator.php
index 0861eea532..f45037d55f 100644
--- a/core/modules/field/src/ProxyClass/FieldUninstallValidator.php
+++ b/core/modules/field/src/ProxyClass/FieldUninstallValidator.php
@@ -60,9 +60,7 @@ public function __construct(\Symfony\Component\DependencyInjection\ContainerInte
          */
         protected function lazyLoadItself()
         {
-            if (!isset($this->service)) {
-                $this->service = $this->container->get($this->drupalProxyOriginalServiceId);
-            }
+              $this->service ??= $this->container->get($this->drupalProxyOriginalServiceId);
 
             return $this->service;
         }
diff --git a/core/modules/file/src/Plugin/views/filter/Status.php b/core/modules/file/src/Plugin/views/filter/Status.php
index 181c3d85a6..e44bcd023f 100644
--- a/core/modules/file/src/Plugin/views/filter/Status.php
+++ b/core/modules/file/src/Plugin/views/filter/Status.php
@@ -15,12 +15,10 @@
 class Status extends InOperator {
 
   public function getValueOptions() {
-    if (!isset($this->valueOptions)) {
-      $this->valueOptions = [
-        0 => $this->t('Temporary'),
-        FileInterface::STATUS_PERMANENT => $this->t('Permanent'),
-      ];
-    }
+    $this->valueOptions ??= [
+      0 => $this->t('Temporary'),
+      FileInterface::STATUS_PERMANENT => $this->t('Permanent'),
+    ];
     return $this->valueOptions;
   }
 
diff --git a/core/modules/file/src/Validation/UploadedFileValidator.php b/core/modules/file/src/Validation/UploadedFileValidator.php
index 984b06f987..c9fce8021d 100644
--- a/core/modules/file/src/Validation/UploadedFileValidator.php
+++ b/core/modules/file/src/Validation/UploadedFileValidator.php
@@ -47,9 +47,7 @@ public function validate(UploadedFile $uploadedFile, array $options = []): Const
    *   The Symfony validator.
    */
   protected function getValidator(): ValidatorInterface {
-    if (!isset($this->validator)) {
-      $this->validator = $this->validatorFactory->createValidator();
-    }
+    $this->validator ??= $this->validatorFactory->createValidator();
     return $this->validator;
   }
 
diff --git a/core/modules/file/tests/src/Functional/FileManagedTestBase.php b/core/modules/file/tests/src/Functional/FileManagedTestBase.php
index aa34b29827..aad51e4782 100644
--- a/core/modules/file/tests/src/Functional/FileManagedTestBase.php
+++ b/core/modules/file/tests/src/Functional/FileManagedTestBase.php
@@ -181,20 +181,16 @@ public function createFile($filepath = NULL, $contents = NULL, $scheme = NULL) {
    *   File URI.
    */
   public function createUri($filepath = NULL, $contents = NULL, $scheme = NULL) {
-    if (!isset($filepath)) {
-      // Prefix with non-latin characters to ensure that all file-related
-      // tests work with international filenames.
-      // cSpell:disable-next-line
-      $filepath = 'Файл для тестирования ' . $this->randomMachineName();
-    }
+    // Prefix with non-latin characters to ensure that all file-related
+    // tests work with international filenames.
+    // cSpell:disable-next-line
+    $filepath ??= 'Файл для тестирования ' . $this->randomMachineName();
     if (!isset($scheme)) {
       $scheme = 'public';
     }
     $filepath = $scheme . '://' . $filepath;
 
-    if (!isset($contents)) {
-      $contents = "file_put_contents() doesn't seem to appreciate empty strings so let's put in some data.";
-    }
+    $contents ??= "file_put_contents() doesn't seem to appreciate empty strings so let's put in some data.";
 
     file_put_contents($filepath, $contents);
     $this->assertFileExists($filepath);
diff --git a/core/modules/file/tests/src/Kernel/FileManagedUnitTestBase.php b/core/modules/file/tests/src/Kernel/FileManagedUnitTestBase.php
index 19ca6f584a..5456116846 100644
--- a/core/modules/file/tests/src/Kernel/FileManagedUnitTestBase.php
+++ b/core/modules/file/tests/src/Kernel/FileManagedUnitTestBase.php
@@ -194,20 +194,16 @@ public function createFile($filepath = NULL, $contents = NULL, $scheme = NULL) {
    *   File URI.
    */
   public function createUri($filepath = NULL, $contents = NULL, $scheme = NULL) {
-    if (!isset($filepath)) {
-      // Prefix with non-latin characters to ensure that all file-related
-      // tests work with international filenames.
-      // cSpell:disable-next-line
-      $filepath = 'Файл для тестирования ' . $this->randomMachineName();
-    }
+    // Prefix with non-latin characters to ensure that all file-related
+    // tests work with international filenames.
+    // cSpell:disable-next-line
+    $filepath ??= 'Файл для тестирования ' . $this->randomMachineName();
     if (!isset($scheme)) {
       $scheme = 'public';
     }
     $filepath = $scheme . '://' . $filepath;
 
-    if (!isset($contents)) {
-      $contents = "file_put_contents() doesn't seem to appreciate empty strings so let's put in some data.";
-    }
+    $contents ??= "file_put_contents() doesn't seem to appreciate empty strings so let's put in some data.";
 
     file_put_contents($filepath, $contents);
     $this->assertFileExists($filepath);
diff --git a/core/modules/filter/filter.module b/core/modules/filter/filter.module
index c6cae99e5a..a5059506db 100644
--- a/core/modules/filter/filter.module
+++ b/core/modules/filter/filter.module
@@ -210,9 +210,7 @@ function filter_get_formats_by_role($rid) {
  * @see filter_fallback_format()
  */
 function filter_default_format(AccountInterface $account = NULL) {
-  if (!isset($account)) {
-    $account = \Drupal::currentUser();
-  }
+  $account ??= \Drupal::currentUser();
   // Get a list of formats for this user, ordered by weight. The first one
   // available is the user's default format.
   $formats = filter_formats($account);
diff --git a/core/modules/filter/src/ProxyClass/FilterUninstallValidator.php b/core/modules/filter/src/ProxyClass/FilterUninstallValidator.php
index 2e7ccc184c..fbc2b4583b 100644
--- a/core/modules/filter/src/ProxyClass/FilterUninstallValidator.php
+++ b/core/modules/filter/src/ProxyClass/FilterUninstallValidator.php
@@ -60,9 +60,7 @@ public function __construct(\Symfony\Component\DependencyInjection\ContainerInte
          */
         protected function lazyLoadItself()
         {
-            if (!isset($this->service)) {
-                $this->service = $this->container->get($this->drupalProxyOriginalServiceId);
-            }
+              $this->service ??= $this->container->get($this->drupalProxyOriginalServiceId);
 
             return $this->service;
         }
diff --git a/core/modules/forum/src/ProxyClass/ForumUninstallValidator.php b/core/modules/forum/src/ProxyClass/ForumUninstallValidator.php
index 7d9469e19f..e832b190a0 100644
--- a/core/modules/forum/src/ProxyClass/ForumUninstallValidator.php
+++ b/core/modules/forum/src/ProxyClass/ForumUninstallValidator.php
@@ -60,9 +60,7 @@ public function __construct(\Symfony\Component\DependencyInjection\ContainerInte
          */
         protected function lazyLoadItself()
         {
-            if (!isset($this->service)) {
-                $this->service = $this->container->get($this->drupalProxyOriginalServiceId);
-            }
+              $this->service ??= $this->container->get($this->drupalProxyOriginalServiceId);
 
             return $this->service;
         }
diff --git a/core/modules/help/src/Plugin/Search/HelpSearch.php b/core/modules/help/src/Plugin/Search/HelpSearch.php
index e59d67549d..58b49ccced 100644
--- a/core/modules/help/src/Plugin/Search/HelpSearch.php
+++ b/core/modules/help/src/Plugin/Search/HelpSearch.php
@@ -277,14 +277,10 @@ protected function prepareResults(StatementInterface $found) {
     $keys = $this->getKeywords();
     foreach ($found as $item) {
       $section_plugin_id = $item->section_plugin_id;
-      if (!isset($plugins[$section_plugin_id])) {
-        $plugins[$section_plugin_id] = $this->getSectionPlugin($section_plugin_id);
-      }
+      $plugins[$section_plugin_id] ??= $this->getSectionPlugin($section_plugin_id);
       if ($plugins[$section_plugin_id]) {
         $langcode = $item->langcode;
-        if (!isset($languages[$langcode])) {
-          $languages[$langcode] = $this->languageManager->getLanguage($item->langcode);
-        }
+        $languages[$langcode] ??= $this->languageManager->getLanguage($item->langcode);
         $topic = $plugins[$section_plugin_id]->renderTopicForSearch($item->topic_id, $languages[$langcode]);
         if ($topic) {
           if (isset($topic['cacheable_metadata'])) {
@@ -346,9 +342,7 @@ public function updateIndex() {
     try {
       foreach ($items as $item) {
         $section_plugin_id = $item->section_plugin_id;
-        if (!isset($section_plugins[$section_plugin_id])) {
-          $section_plugins[$section_plugin_id] = $this->getSectionPlugin($section_plugin_id);
-        }
+        $section_plugins[$section_plugin_id] ??= $this->getSectionPlugin($section_plugin_id);
 
         if (!$section_plugins[$section_plugin_id]) {
           $this->removeItemsFromIndex($item->sid);
diff --git a/core/modules/history/history.module b/core/modules/history/history.module
index 2870e37b88..5811234b9e 100644
--- a/core/modules/history/history.module
+++ b/core/modules/history/history.module
@@ -105,9 +105,7 @@ function history_read_multiple($nids) {
  */
 function history_write($nid, $account = NULL) {
 
-  if (!isset($account)) {
-    $account = \Drupal::currentUser();
-  }
+  $account ??= \Drupal::currentUser();
 
   if ($account->isAuthenticated()) {
     $request_time = \Drupal::time()->getRequestTime();
diff --git a/core/modules/image/src/Form/ImageStyleDeleteForm.php b/core/modules/image/src/Form/ImageStyleDeleteForm.php
index a0aea333b5..0fa96cc0db 100644
--- a/core/modules/image/src/Form/ImageStyleDeleteForm.php
+++ b/core/modules/image/src/Form/ImageStyleDeleteForm.php
@@ -77,9 +77,7 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
    *   An option list suitable for the form select '#options'.
    */
   protected function getReplacementOptions() {
-    if (!isset($this->replacementOptions)) {
-      $this->replacementOptions = array_diff_key(image_style_options(), [$this->getEntity()->id() => '']);
-    }
+    $this->replacementOptions ??= array_diff_key(image_style_options(), [$this->getEntity()->id() => '']);
     return $this->replacementOptions;
   }
 
diff --git a/core/modules/jsonapi/src/JsonApiResource/ResourceIdentifierTrait.php b/core/modules/jsonapi/src/JsonApiResource/ResourceIdentifierTrait.php
index b7b65586e5..cec970247d 100644
--- a/core/modules/jsonapi/src/JsonApiResource/ResourceIdentifierTrait.php
+++ b/core/modules/jsonapi/src/JsonApiResource/ResourceIdentifierTrait.php
@@ -47,9 +47,7 @@ public function getTypeName() {
    * {@inheritdoc}
    */
   public function getResourceType() {
-    if (!isset($this->resourceType)) {
-      $this->resourceType = $this->resourceIdentifier->getResourceType();
-    }
+    $this->resourceType ??= $this->resourceIdentifier->getResourceType();
     return $this->resourceType;
   }
 
diff --git a/core/modules/jsonapi/src/Query/Filter.php b/core/modules/jsonapi/src/Query/Filter.php
index ab134317c4..a2ada166b1 100644
--- a/core/modules/jsonapi/src/Query/Filter.php
+++ b/core/modules/jsonapi/src/Query/Filter.php
@@ -232,9 +232,7 @@ protected static function expand(array $original) {
    */
   protected static function expandItem($filter_index, array $filter_item) {
     if (isset($filter_item[EntityCondition::VALUE_KEY])) {
-      if (!isset($filter_item[EntityCondition::PATH_KEY])) {
-        $filter_item[EntityCondition::PATH_KEY] = $filter_index;
-      }
+      $filter_item[EntityCondition::PATH_KEY] ??= $filter_index;
 
       $filter_item = [
         static::CONDITION_KEY => $filter_item,
@@ -242,9 +240,7 @@ protected static function expandItem($filter_index, array $filter_item) {
       ];
     }
 
-    if (!isset($filter_item[static::CONDITION_KEY][EntityCondition::OPERATOR_KEY])) {
-      $filter_item[static::CONDITION_KEY][EntityCondition::OPERATOR_KEY] = '=';
-    }
+    $filter_item[static::CONDITION_KEY][EntityCondition::OPERATOR_KEY] ??= '=';
 
     return $filter_item;
   }
diff --git a/core/modules/jsonapi/tests/src/Functional/ResourceResponseTestTrait.php b/core/modules/jsonapi/tests/src/Functional/ResourceResponseTestTrait.php
index 993ff5b57b..49d6a7321b 100644
--- a/core/modules/jsonapi/tests/src/Functional/ResourceResponseTestTrait.php
+++ b/core/modules/jsonapi/tests/src/Functional/ResourceResponseTestTrait.php
@@ -90,9 +90,7 @@ protected static function toCollectionResourceResponse(array $responses, $self_l
       unset($merged_document['links']);
     }
     else {
-      if (!isset($merged_document['data'])) {
-        $merged_document['data'] = $is_multiple ? [] : NULL;
-      }
+      $merged_document['data'] ??= $is_multiple ? [] : NULL;
       $merged_document['links'] = [
         'self' => [
           'href' => $self_link,
diff --git a/core/modules/jsonapi/tests/src/Functional/ResourceTestBase.php b/core/modules/jsonapi/tests/src/Functional/ResourceTestBase.php
index be0c633adc..184df68b4e 100644
--- a/core/modules/jsonapi/tests/src/Functional/ResourceTestBase.php
+++ b/core/modules/jsonapi/tests/src/Functional/ResourceTestBase.php
@@ -1257,9 +1257,7 @@ protected function getExpectedCollectionResponse(array $collection, $self_link,
     $merged_response = static::toCollectionResourceResponse($individual_responses, $self_link, TRUE);
 
     $merged_document = $merged_response->getResponseData();
-    if (!isset($merged_document['data'])) {
-      $merged_document['data'] = [];
-    }
+    $merged_document['data'] ??= [];
 
     $cacheability = static::getExpectedCollectionCacheability($this->account, $collection, NULL, $filtered);
     $cacheability->setCacheMaxAge($merged_response->getCacheableMetadata()->getCacheMaxAge());
diff --git a/core/modules/language/language.module b/core/modules/language/language.module
index 4ac86e6802..0180e5c1e0 100644
--- a/core/modules/language/language.module
+++ b/core/modules/language/language.module
@@ -122,12 +122,8 @@ function language_element_info_alter(&$type) {
   // Alter the language_select element so that it will be rendered like a select
   // field.
   if (isset($type['language_select'])) {
-    if (!isset($type['language_select']['#process'])) {
-      $type['language_select']['#process'] = [];
-    }
-    if (!isset($type['language_select']['#theme_wrappers'])) {
-      $type['language_select']['#theme_wrappers'] = [];
-    }
+    $type['language_select']['#process'] ??= [];
+    $type['language_select']['#theme_wrappers'] ??= [];
     $type['language_select']['#process'] = array_merge($type['language_select']['#process'], [
       'language_process_language_select',
       ['Drupal\Core\Render\Element\Select', 'processSelect'],
diff --git a/core/modules/language/src/Config/LanguageConfigFactoryOverride.php b/core/modules/language/src/Config/LanguageConfigFactoryOverride.php
index 67ae7dfa99..eb4f6e627b 100644
--- a/core/modules/language/src/Config/LanguageConfigFactoryOverride.php
+++ b/core/modules/language/src/Config/LanguageConfigFactoryOverride.php
@@ -115,9 +115,7 @@ public function getOverride($langcode, $name) {
    * {@inheritdoc}
    */
   public function getStorage($langcode) {
-    if (!isset($this->storages[$langcode])) {
-      $this->storages[$langcode] = $this->baseStorage->createCollection($this->createConfigCollectionName($langcode));
-    }
+    $this->storages[$langcode] ??= $this->baseStorage->createCollection($this->createConfigCollectionName($langcode));
     return $this->storages[$langcode];
   }
 
diff --git a/core/modules/language/src/Form/NegotiationConfigureForm.php b/core/modules/language/src/Form/NegotiationConfigureForm.php
index d25305f030..75ce4781fa 100644
--- a/core/modules/language/src/Form/NegotiationConfigureForm.php
+++ b/core/modules/language/src/Form/NegotiationConfigureForm.php
@@ -251,9 +251,7 @@ protected function configureFormTable(array &$form, $type) {
 
     // Add missing data to the methods lists.
     foreach ($negotiation_info as $method_id => $method) {
-      if (!isset($methods_weight[$method_id])) {
-        $methods_weight[$method_id] = $method['weight'] ?? 0;
-      }
+      $methods_weight[$method_id] ??= $method['weight'] ?? 0;
     }
 
     // Order methods list by weight.
diff --git a/core/modules/language/src/HttpKernel/PathProcessorLanguage.php b/core/modules/language/src/HttpKernel/PathProcessorLanguage.php
index 3aed7ecc2a..550b0c71f7 100644
--- a/core/modules/language/src/HttpKernel/PathProcessorLanguage.php
+++ b/core/modules/language/src/HttpKernel/PathProcessorLanguage.php
@@ -102,9 +102,7 @@ public function processInbound($path, Request $request) {
    * {@inheritdoc}
    */
   public function processOutbound($path, &$options = [], Request $request = NULL, BubbleableMetadata $bubbleable_metadata = NULL) {
-    if (!isset($this->multilingual)) {
-      $this->multilingual = $this->languageManager->isMultilingual();
-    }
+    $this->multilingual ??= $this->languageManager->isMultilingual();
     if ($this->multilingual) {
       $this->negotiator->reset();
       $scope = 'outbound';
diff --git a/core/modules/language/src/Plugin/LanguageNegotiation/LanguageNegotiationContentEntity.php b/core/modules/language/src/Plugin/LanguageNegotiation/LanguageNegotiationContentEntity.php
index 12f349a461..b3d833b53e 100644
--- a/core/modules/language/src/Plugin/LanguageNegotiation/LanguageNegotiationContentEntity.php
+++ b/core/modules/language/src/Plugin/LanguageNegotiation/LanguageNegotiationContentEntity.php
@@ -121,9 +121,7 @@ public function processOutbound($path, &$options = [], Request $request = NULL,
         unset($options['language']);
       }
 
-      if (!isset($options['query'][static::QUERY_PARAMETER])) {
-        $options['query'][static::QUERY_PARAMETER] = $langcode;
-      }
+      $options['query'][static::QUERY_PARAMETER] ??= $langcode;
 
       if ($bubbleable_metadata) {
         // Cached URLs that have been processed by this outbound path
diff --git a/core/modules/language/src/Plugin/LanguageNegotiation/LanguageNegotiationSession.php b/core/modules/language/src/Plugin/LanguageNegotiation/LanguageNegotiationSession.php
index daa8cf8acd..ee6ee69ffa 100644
--- a/core/modules/language/src/Plugin/LanguageNegotiation/LanguageNegotiationSession.php
+++ b/core/modules/language/src/Plugin/LanguageNegotiation/LanguageNegotiationSession.php
@@ -136,9 +136,7 @@ public function processOutbound($path, &$options = [], Request $request = NULL,
       // enabled, and the corresponding option has been set, we must preserve
       // any explicit user language preference even with cookies disabled.
       if ($this->queryRewrite) {
-        if (!isset($options['query'][$this->queryParam])) {
-          $options['query'][$this->queryParam] = $this->queryValue;
-        }
+        $options['query'][$this->queryParam] ??= $this->queryValue;
         if ($bubbleable_metadata) {
           // Cached URLs that have been processed by this outbound path
           // processor must be:
diff --git a/core/modules/language/src/ProxyClass/LanguageConverter.php b/core/modules/language/src/ProxyClass/LanguageConverter.php
index 5511c6859e..dfa7867771 100644
--- a/core/modules/language/src/ProxyClass/LanguageConverter.php
+++ b/core/modules/language/src/ProxyClass/LanguageConverter.php
@@ -60,9 +60,7 @@ public function __construct(\Symfony\Component\DependencyInjection\ContainerInte
          */
         protected function lazyLoadItself()
         {
-            if (!isset($this->service)) {
-                $this->service = $this->container->get($this->drupalProxyOriginalServiceId);
-            }
+              $this->service ??= $this->container->get($this->drupalProxyOriginalServiceId);
 
             return $this->service;
         }
diff --git a/core/modules/language/tests/language_events_test/src/EventSubscriber.php b/core/modules/language/tests/language_events_test/src/EventSubscriber.php
index e805b9fc62..81c39ce616 100644
--- a/core/modules/language/tests/language_events_test/src/EventSubscriber.php
+++ b/core/modules/language/tests/language_events_test/src/EventSubscriber.php
@@ -37,9 +37,7 @@ public function configEventRecorder(LanguageConfigOverrideCrudEvent $event, stri
     // Record all events that occur.
     $all_events = $this->state->get('language_events_test.all_events', []);
     $override_name = $override->getName();
-    if (!isset($all_events[$event_name][$override_name])) {
-      $all_events[$event_name][$override_name] = [];
-    }
+    $all_events[$event_name][$override_name] ??= [];
     $all_events[$event_name][$override_name][] = $event_info;
     $this->state->set('language_events_test.all_events', $all_events);
   }
diff --git a/core/modules/layout_builder/src/Form/MoveBlockForm.php b/core/modules/layout_builder/src/Form/MoveBlockForm.php
index beb3aa9757..ed8f21b1a5 100644
--- a/core/modules/layout_builder/src/Form/MoveBlockForm.php
+++ b/core/modules/layout_builder/src/Form/MoveBlockForm.php
@@ -187,9 +187,7 @@ public function buildForm(array $form, FormStateInterface $form_state, SectionSt
     $components = $current_section->getComponentsByRegion($selected_region);
 
     // If the component is not in this region, add it to the listed components.
-    if (!isset($components[$uuid])) {
-      $components[$uuid] = $sections[$delta]->getComponent($uuid);
-    }
+    $components[$uuid] ??= $sections[$delta]->getComponent($uuid);
     $state_weight_delta = round(count($components) / 2);
     foreach ($components as $component_uuid => $component) {
       /** @var \Drupal\Core\Block\BlockPluginInterface $plugin */
diff --git a/core/modules/layout_discovery/layout_discovery.module b/core/modules/layout_discovery/layout_discovery.module
index 02bedc5353..262d918909 100644
--- a/core/modules/layout_discovery/layout_discovery.module
+++ b/core/modules/layout_discovery/layout_discovery.module
@@ -43,9 +43,7 @@ function template_preprocess_layout(&$variables) {
 
   // Create an attributes variable for each region.
   foreach (Element::children($variables['content']) as $name) {
-    if (!isset($variables['content'][$name]['#attributes'])) {
-      $variables['content'][$name]['#attributes'] = [];
-    }
+    $variables['content'][$name]['#attributes'] ??= [];
     $variables['region_attributes'][$name] = new Attribute($variables['content'][$name]['#attributes']);
   }
 }
diff --git a/core/modules/locale/locale.bulk.inc b/core/modules/locale/locale.bulk.inc
index b5e3270cea..f6f71109b0 100644
--- a/core/modules/locale/locale.bulk.inc
+++ b/core/modules/locale/locale.bulk.inc
@@ -246,9 +246,7 @@ function locale_translate_batch_import($file, array $options, &$context) {
       }
       foreach ($report as $key => $value) {
         if (is_numeric($report[$key])) {
-          if (!isset($context['results']['stats'][$file->uri][$key])) {
-            $context['results']['stats'][$file->uri][$key] = 0;
-          }
+          $context['results']['stats'][$file->uri][$key] ??= 0;
           $context['results']['stats'][$file->uri][$key] += $report[$key];
         }
         elseif (is_array($value)) {
@@ -638,9 +636,7 @@ function locale_config_batch_set_config_langcodes(&$context) {
  * @see locale_config_batch_build()
  */
 function locale_config_batch_refresh_name(array $names, array $langcodes, &$context) {
-  if (!isset($context['results']['stats']['config'])) {
-    $context['results']['stats']['config'] = 0;
-  }
+  $context['results']['stats']['config'] ??= 0;
   $context['results']['stats']['config'] += Locale::config()->updateConfigTranslations($names, $langcodes);
   foreach ($names as $name) {
     $context['results']['names'][] = $name;
diff --git a/core/modules/locale/locale.module b/core/modules/locale/locale.module
index 093823a29e..254fab0823 100644
--- a/core/modules/locale/locale.module
+++ b/core/modules/locale/locale.module
@@ -515,9 +515,7 @@ function locale_js_alter(&$javascript, AttachedAssetsInterface $assets, Language
  *   applicable.
  */
 function locale_js_translate(array $files = [], $language_interface = NULL) {
-  if (!isset($language_interface)) {
-    $language_interface = \Drupal::languageManager()->getCurrentLanguage();
-  }
+  $language_interface ??= \Drupal::languageManager()->getCurrentLanguage();
 
   $dir = 'public://' . \Drupal::config('locale.settings')->get('javascript.directory');
   $parsed = \Drupal::state()->get('system.javascript_parsed', []);
diff --git a/core/modules/locale/src/LocaleTranslation.php b/core/modules/locale/src/LocaleTranslation.php
index a9ccc93626..ba7cd8882a 100644
--- a/core/modules/locale/src/LocaleTranslation.php
+++ b/core/modules/locale/src/LocaleTranslation.php
@@ -115,9 +115,7 @@ public function getStringTranslation($langcode, $string, $context) {
     }
     // Strings are cached by langcode, context and roles, using instances of the
     // LocaleLookup class to handle string lookup and caching.
-    if (!isset($this->translations[$langcode][$context])) {
-      $this->translations[$langcode][$context] = new LocaleLookup($langcode, $context, $this->storage, $this->cache, $this->lock, $this->configFactory, $this->languageManager, $this->requestStack);
-    }
+    $this->translations[$langcode][$context] ??= new LocaleLookup($langcode, $context, $this->storage, $this->cache, $this->lock, $this->configFactory, $this->languageManager, $this->requestStack);
     $translation = $this->translations[$langcode][$context]->get($string);
     // If the translation is TRUE, no translation exists, but that string needs
     // to be stored in the persistent cache for performance reasons (so for
@@ -134,9 +132,7 @@ public function getStringTranslation($langcode, $string, $context) {
    *   TRUE if english should be translated, FALSE if not.
    */
   protected function canTranslateEnglish() {
-    if (!isset($this->translateEnglish)) {
-      $this->translateEnglish = $this->configFactory->get('locale.settings')->get('translate_english');
-    }
+    $this->translateEnglish ??= $this->configFactory->get('locale.settings')->get('translate_english');
     return $this->translateEnglish;
   }
 
diff --git a/core/modules/locale/src/PoDatabaseReader.php b/core/modules/locale/src/PoDatabaseReader.php
index 4ed7663467..4e946b34d3 100644
--- a/core/modules/locale/src/PoDatabaseReader.php
+++ b/core/modules/locale/src/PoDatabaseReader.php
@@ -150,9 +150,7 @@ private function loadStrings() {
    * Get the database result resource for the given language and options.
    */
   private function readString() {
-    if (!isset($this->result)) {
-      $this->result = $this->loadStrings();
-    }
+    $this->result ??= $this->loadStrings();
     return array_shift($this->result);
   }
 
diff --git a/core/modules/locale/src/PoDatabaseWriter.php b/core/modules/locale/src/PoDatabaseWriter.php
index 7e7340cf10..7720039fb6 100644
--- a/core/modules/locale/src/PoDatabaseWriter.php
+++ b/core/modules/locale/src/PoDatabaseWriter.php
@@ -121,9 +121,7 @@ public function getOptions() {
    *     One of LOCALE_CUSTOMIZED or LOCALE_NOT_CUSTOMIZED.
    */
   public function setOptions(array $options) {
-    if (!isset($options['overwrite_options'])) {
-      $options['overwrite_options'] = [];
-    }
+    $options['overwrite_options'] ??= [];
     $options['overwrite_options'] += [
       'not_customized' => FALSE,
       'customized' => FALSE,
diff --git a/core/modules/locale/src/TranslationString.php b/core/modules/locale/src/TranslationString.php
index ac8ef1440b..2644596ed8 100644
--- a/core/modules/locale/src/TranslationString.php
+++ b/core/modules/locale/src/TranslationString.php
@@ -44,12 +44,10 @@ class TranslationString extends StringBase {
    */
   public function __construct($values = []) {
     parent::__construct($values);
-    if (!isset($this->isNew)) {
-      // We mark the string as not new if it is a complete translation.
-      // This will work when loading from database, otherwise the storage
-      // controller that creates the string object must handle it.
-      $this->isNew = !$this->isTranslation();
-    }
+    // We mark the string as not new if it is a complete translation.
+    // This will work when loading from database, otherwise the storage
+    // controller that creates the string object must handle it.
+    $this->isNew ??= !$this->isTranslation();
   }
 
   /**
diff --git a/core/modules/menu_ui/src/MenuForm.php b/core/modules/menu_ui/src/MenuForm.php
index 9d90ac5a60..d847989c60 100644
--- a/core/modules/menu_ui/src/MenuForm.php
+++ b/core/modules/menu_ui/src/MenuForm.php
@@ -451,10 +451,8 @@ protected function buildOverviewTreeForm($tree, $delta) {
           uasort($operations, [SortArray::class, 'sortByWeightElement']);
         }
         foreach ($operations as $key => $operation) {
-          if (!isset($operations[$key]['query'])) {
-            // Bring the user back to the menu overview.
-            $operations[$key]['query'] = $this->getDestinationArray();
-          }
+          // Bring the user back to the menu overview.
+          $operations[$key]['query'] ??= $this->getDestinationArray();
         }
         $form[$id]['operations'] = [
           '#type' => 'operations',
diff --git a/core/modules/migrate/src/MigrateExecutable.php b/core/modules/migrate/src/MigrateExecutable.php
index 47b887f376..1d6578ff60 100644
--- a/core/modules/migrate/src/MigrateExecutable.php
+++ b/core/modules/migrate/src/MigrateExecutable.php
@@ -125,9 +125,7 @@ public function __construct(MigrationInterface $migration, MigrateMessageInterfa
    *   The source.
    */
   protected function getSource() {
-    if (!isset($this->source)) {
-      $this->source = $this->migration->getSourcePlugin();
-    }
+    $this->source ??= $this->migration->getSourcePlugin();
     return $this->source;
   }
 
diff --git a/core/modules/migrate/src/Plugin/Migration.php b/core/modules/migrate/src/Plugin/Migration.php
index f19a35e3e5..1f49e07930 100644
--- a/core/modules/migrate/src/Plugin/Migration.php
+++ b/core/modules/migrate/src/Plugin/Migration.php
@@ -388,9 +388,7 @@ public function getIdMapPlugin() {
    * {@inheritdoc}
    */
   public function getSourcePlugin() {
-    if (!isset($this->sourcePlugin)) {
-      $this->sourcePlugin = $this->sourcePluginManager->createInstance($this->source['plugin'], $this->source, $this);
-    }
+    $this->sourcePlugin ??= $this->sourcePluginManager->createInstance($this->source['plugin'], $this->source, $this);
     return $this->sourcePlugin;
   }
 
@@ -398,9 +396,7 @@ public function getSourcePlugin() {
    * {@inheritdoc}
    */
   public function getProcessPlugins(array $process = NULL) {
-    if (!isset($process)) {
-      $process = $this->getProcess();
-    }
+    $process ??= $this->getProcess();
     $index = serialize($process);
     if (!isset($this->processPlugins[$index])) {
       $this->processPlugins[$index] = [];
@@ -460,9 +456,7 @@ public function getDestinationPlugin($stub_being_requested = FALSE) {
     if ($stub_being_requested && !empty($this->destination['no_stub'])) {
       throw new MigrateSkipRowException('Stub requested but not made because no_stub configuration is set.');
     }
-    if (!isset($this->destinationPlugin)) {
-      $this->destinationPlugin = $this->destinationPluginManager->createInstance($this->destination['plugin'], $this->destination, $this);
-    }
+    $this->destinationPlugin ??= $this->destinationPluginManager->createInstance($this->destination['plugin'], $this->destination, $this);
     return $this->destinationPlugin;
   }
 
diff --git a/core/modules/migrate/src/Plugin/MigrationPluginManager.php b/core/modules/migrate/src/Plugin/MigrationPluginManager.php
index 8725ac4756..65c4588e61 100644
--- a/core/modules/migrate/src/Plugin/MigrationPluginManager.php
+++ b/core/modules/migrate/src/Plugin/MigrationPluginManager.php
@@ -227,9 +227,7 @@ public function buildDependencyMigration(array $migrations, array $dynamic_ids)
    */
   protected function addDependency(array &$graph, $id, $dependency, $dynamic_ids) {
     $dependencies = $dynamic_ids[$dependency] ?? [$dependency];
-    if (!isset($graph[$id]['edges'])) {
-      $graph[$id]['edges'] = [];
-    }
+    $graph[$id]['edges'] ??= [];
     $graph[$id]['edges'] += array_combine($dependencies, $dependencies);
   }
 
diff --git a/core/modules/migrate/src/Plugin/migrate/id_map/Sql.php b/core/modules/migrate/src/Plugin/migrate/id_map/Sql.php
index 52b89c9999..f9319469c1 100644
--- a/core/modules/migrate/src/Plugin/migrate/id_map/Sql.php
+++ b/core/modules/migrate/src/Plugin/migrate/id_map/Sql.php
@@ -176,9 +176,7 @@ public function __construct(array $configuration, $plugin_id, $plugin_definition
     $this->eventDispatcher = $event_dispatcher;
     $this->message = new MigrateMessage();
 
-    if (!isset($this->database)) {
-      $this->database = \Drupal::database();
-    }
+    $this->database ??= \Drupal::database();
 
     // Default generated table names, limited to 63 characters.
     $machine_name = str_replace(':', '__', $this->migration->id());
diff --git a/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php b/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php
index 3191c7256d..aede29e1e2 100644
--- a/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php
+++ b/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php
@@ -280,9 +280,7 @@ abstract protected function initializeIterator();
    *   The module handler.
    */
   protected function getModuleHandler() {
-    if (!isset($this->moduleHandler)) {
-      $this->moduleHandler = \Drupal::moduleHandler();
-    }
+    $this->moduleHandler ??= \Drupal::moduleHandler();
     return $this->moduleHandler;
   }
 
@@ -334,9 +332,7 @@ public function prepareRow(Row $row) {
    *   The iterator that will yield the row arrays to be processed.
    */
   protected function getIterator() {
-    if (!isset($this->iterator)) {
-      $this->iterator = $this->initializeIterator();
-    }
+    $this->iterator ??= $this->initializeIterator();
     return $this->iterator;
   }
 
@@ -521,9 +517,7 @@ public function count($refresh = FALSE) {
    *   The cache object.
    */
   protected function getCache() {
-    if (!isset($this->cache)) {
-      $this->cache = \Drupal::cache('migrate');
-    }
+    $this->cache ??= \Drupal::cache('migrate');
     return $this->cache;
   }
 
@@ -546,9 +540,7 @@ protected function doCount() {
    *   The storage object.
    */
   protected function getHighWaterStorage() {
-    if (!isset($this->highWaterStorage)) {
-      $this->highWaterStorage = \Drupal::keyValue('migrate:high_water');
-    }
+    $this->highWaterStorage ??= \Drupal::keyValue('migrate:high_water');
     return $this->highWaterStorage;
   }
 
diff --git a/core/modules/mysql/src/Driver/Database/mysql/Schema.php b/core/modules/mysql/src/Driver/Database/mysql/Schema.php
index 6fdcad7047..7f6d999960 100644
--- a/core/modules/mysql/src/Driver/Database/mysql/Schema.php
+++ b/core/modules/mysql/src/Driver/Database/mysql/Schema.php
@@ -204,9 +204,7 @@ protected function createFieldSql($name, $spec) {
    */
   protected function processField($field) {
 
-    if (!isset($field['size'])) {
-      $field['size'] = 'normal';
-    }
+    $field['size'] ??= 'normal';
 
     // Set the correct database-engine specific datatype.
     // In case one is already provided, force it to uppercase.
diff --git a/core/modules/node/src/Plugin/Search/NodeSearch.php b/core/modules/node/src/Plugin/Search/NodeSearch.php
index a58487c1da..533f25baa9 100644
--- a/core/modules/node/src/Plugin/Search/NodeSearch.php
+++ b/core/modules/node/src/Plugin/Search/NodeSearch.php
@@ -758,9 +758,7 @@ protected function parseAdvancedDefaults($f, $keys) {
     // Split out the advanced search parameters.
     foreach ($f as $advanced) {
       [$key, $value] = explode(':', $advanced, 2);
-      if (!isset($defaults[$key])) {
-        $defaults[$key] = [];
-      }
+      $defaults[$key] ??= [];
       $defaults[$key][] = $value;
     }
 
diff --git a/core/modules/node/src/ProxyClass/ParamConverter/NodePreviewConverter.php b/core/modules/node/src/ProxyClass/ParamConverter/NodePreviewConverter.php
index 7dcd43e7ca..193143bb51 100644
--- a/core/modules/node/src/ProxyClass/ParamConverter/NodePreviewConverter.php
+++ b/core/modules/node/src/ProxyClass/ParamConverter/NodePreviewConverter.php
@@ -60,9 +60,7 @@ public function __construct(\Symfony\Component\DependencyInjection\ContainerInte
          */
         protected function lazyLoadItself()
         {
-            if (!isset($this->service)) {
-                $this->service = $this->container->get($this->drupalProxyOriginalServiceId);
-            }
+              $this->service ??= $this->container->get($this->drupalProxyOriginalServiceId);
 
             return $this->service;
         }
diff --git a/core/modules/options/src/Plugin/Field/FieldType/ListStringItem.php b/core/modules/options/src/Plugin/Field/FieldType/ListStringItem.php
index 22cd0d9ac6..68de94839d 100644
--- a/core/modules/options/src/Plugin/Field/FieldType/ListStringItem.php
+++ b/core/modules/options/src/Plugin/Field/FieldType/ListStringItem.php
@@ -121,9 +121,7 @@ public static function processAllowedValuesKey(array &$element): array {
     // Override the default description which is not applicable to this use of
     // the machine name element given that it allows users to manually enter
     // characters usually not allowed in machine names.
-    if (!isset($element['#description'])) {
-      $element['#description'] = '';
-    }
+    $element['#description'] ??= '';
 
     return $element;
   }
diff --git a/core/modules/pgsql/src/Driver/Database/pgsql/Schema.php b/core/modules/pgsql/src/Driver/Database/pgsql/Schema.php
index 2ff57aebee..c0f4127bb0 100644
--- a/core/modules/pgsql/src/Driver/Database/pgsql/Schema.php
+++ b/core/modules/pgsql/src/Driver/Database/pgsql/Schema.php
@@ -206,9 +206,7 @@ public function queryTableInformation($table) {
    *   PostgreSQL's temporary namespace name.
    */
   protected function getTempNamespaceName() {
-    if (!isset($this->tempNamespaceName)) {
-      $this->tempNamespaceName = $this->connection->query('SELECT nspname FROM pg_namespace WHERE oid = pg_my_temp_schema()')->fetchField();
-    }
+    $this->tempNamespaceName ??= $this->connection->query('SELECT nspname FROM pg_namespace WHERE oid = pg_my_temp_schema()')->fetchField();
     return $this->tempNamespaceName;
   }
 
@@ -384,9 +382,7 @@ protected function createFieldSql($name, $spec) {
    *   A field description array, as specified in the schema documentation.
    */
   protected function processField($field) {
-    if (!isset($field['size'])) {
-      $field['size'] = 'normal';
-    }
+    $field['size'] ??= 'normal';
 
     // Set the correct database-engine specific datatype.
     // In case one is already provided, force it to lowercase.
@@ -405,9 +401,7 @@ protected function processField($field) {
       // The PostgreSQL schema in Drupal creates a check constraint
       // to ensure that a value inserted is >= 0. To provide the extra
       // integer capacity, here, we bump up the column field size.
-      if (!isset($map)) {
-        $map = $this->getFieldTypeMap();
-      }
+      $map ??= $this->getFieldTypeMap();
       switch ($field['pgsql_type']) {
         case 'smallint':
           $field['pgsql_type'] = $map['int:medium'];
diff --git a/core/modules/rest/src/Entity/RestResourceConfig.php b/core/modules/rest/src/Entity/RestResourceConfig.php
index 027eb5e6c5..515a3b5fb3 100644
--- a/core/modules/rest/src/Entity/RestResourceConfig.php
+++ b/core/modules/rest/src/Entity/RestResourceConfig.php
@@ -93,9 +93,7 @@ public function __construct(array $values, $entity_type) {
    * @return \Drupal\Component\Plugin\PluginManagerInterface
    */
   protected function getResourcePluginManager() {
-    if (!isset($this->pluginManager)) {
-      $this->pluginManager = \Drupal::service('plugin.manager.rest');
-    }
+    $this->pluginManager ??= \Drupal::service('plugin.manager.rest');
     return $this->pluginManager;
   }
 
diff --git a/core/modules/sdc/src/Twig/TwigExtension.php b/core/modules/sdc/src/Twig/TwigExtension.php
index 8205080cb0..7fa2d511c3 100644
--- a/core/modules/sdc/src/Twig/TwigExtension.php
+++ b/core/modules/sdc/src/Twig/TwigExtension.php
@@ -87,9 +87,7 @@ public function addAdditionalContext(array &$context, string $component_id): voi
   protected function mergeAdditionalRenderContext(Component $component, array $context): array {
     $context['componentMetadata'] = $component->metadata->normalize();
     $component_attributes = ['data-component-id' => $component->getPluginId()];
-    if (!isset($context['attributes'])) {
-      $context['attributes'] = new Attribute($component_attributes);
-    }
+    $context['attributes'] ??= new Attribute($component_attributes);
     // If there is an "attributes" property, merge the additional attributes
     // into it if possible.
     elseif ($context['attributes'] instanceof Attribute) {
diff --git a/core/modules/search/search.api.php b/core/modules/search/search.api.php
index 47744998e3..1d4a295eaf 100644
--- a/core/modules/search/search.api.php
+++ b/core/modules/search/search.api.php
@@ -48,9 +48,7 @@
  */
 function hook_search_preprocess($text, $langcode = NULL) {
   // If the language is not set, get it from the language manager.
-  if (!isset($langcode)) {
-    $langcode = \Drupal::languageManager()->getCurrentLanguage()->getId();
-  }
+  $langcode ??= \Drupal::languageManager()->getCurrentLanguage()->getId();
 
   // If the langcode is set to 'en' then add variations of the word "testing"
   // which can also be found during English language searches.
diff --git a/core/modules/search/search.module b/core/modules/search/search.module
index 84feabfed8..06ffe21cc0 100644
--- a/core/modules/search/search.module
+++ b/core/modules/search/search.module
@@ -178,9 +178,7 @@ function search_excerpt($keys, $text, $langcode = NULL) {
 
       // Remember where we last found $key, in case we are coming through a
       // second time.
-      if (!isset($look_start[$key])) {
-        $look_start[$key] = 0;
-      }
+      $look_start[$key] ??= 0;
 
       // See if we can find $key after where we found it the last time. Since
       // we are requiring a match on a word boundary, make sure $text starts
diff --git a/core/modules/search/src/Entity/SearchPage.php b/core/modules/search/src/Entity/SearchPage.php
index d5eef74a9c..883e7eb2ee 100644
--- a/core/modules/search/src/Entity/SearchPage.php
+++ b/core/modules/search/src/Entity/SearchPage.php
@@ -182,9 +182,7 @@ public function postCreate(EntityStorageInterface $storage) {
 
     // @todo Use self::applyDefaultValue() once
     //   https://www.drupal.org/node/2004756 is in.
-    if (!isset($this->weight)) {
-      $this->weight = $this->isDefaultSearch() ? -10 : 0;
-    }
+    $this->weight ??= $this->isDefaultSearch() ? -10 : 0;
   }
 
   /**
diff --git a/core/modules/search/src/SearchIndex.php b/core/modules/search/src/SearchIndex.php
index 97f57abe12..999060429b 100644
--- a/core/modules/search/src/SearchIndex.php
+++ b/core/modules/search/src/SearchIndex.php
@@ -155,9 +155,7 @@ public function index($type, $sid, $langcode, $text, $update_weights = TRUE) {
             $accumulator .= $word . ' ';
             // Check word length.
             if (is_numeric($word) || mb_strlen($word) >= $minimum_word_size) {
-              if (!isset($scored_words[$word])) {
-                $scored_words[$word] = 0;
-              }
+              $scored_words[$word] ??= 0;
               $scored_words[$word] += $score * $focus;
               // Focus is a decaying value in terms of the amount of unique
               // words up to this point. From 100 words and more, it decays, to
diff --git a/core/modules/settings_tray/settings_tray.module b/core/modules/settings_tray/settings_tray.module
index 35a4466575..934c5d4bdb 100644
--- a/core/modules/settings_tray/settings_tray.module
+++ b/core/modules/settings_tray/settings_tray.module
@@ -169,9 +169,7 @@ function settings_tray_block_alter(&$definitions) {
   foreach ($definitions as &$definition) {
     // If a block plugin does not define its own 'settings_tray' form, use the
     // plugin class itself.
-    if (!isset($definition['forms']['settings_tray'])) {
-      $definition['forms']['settings_tray'] = $definition['class'];
-    }
+    $definition['forms']['settings_tray'] ??= $definition['class'];
   }
 }
 
diff --git a/core/modules/shortcut/shortcut.module b/core/modules/shortcut/shortcut.module
index df1b9969c3..00a6701605 100644
--- a/core/modules/shortcut/shortcut.module
+++ b/core/modules/shortcut/shortcut.module
@@ -131,9 +131,7 @@ function shortcut_set_switch_access($account = NULL) {
 function shortcut_current_displayed_set($account = NULL) {
   $shortcut_sets = &drupal_static(__FUNCTION__, []);
   $user = \Drupal::currentUser();
-  if (!isset($account)) {
-    $account = $user;
-  }
+  $account ??= $user;
   // Try to return a shortcut set from the static cache.
   if (isset($shortcut_sets[$account->id()])) {
     return $shortcut_sets[$account->id()];
@@ -168,9 +166,7 @@ function shortcut_current_displayed_set($account = NULL) {
  */
 function shortcut_default_set($account = NULL) {
   $user = \Drupal::currentUser();
-  if (!isset($account)) {
-    $account = $user;
-  }
+  $account ??= $user;
 
   // Allow modules to return a default shortcut set name. Since we can only
   // have one, we allow the last module which returns a valid result to take
@@ -200,9 +196,7 @@ function shortcut_default_set($account = NULL) {
 function shortcut_renderable_links($shortcut_set = NULL) {
   $shortcut_links = [];
 
-  if (!isset($shortcut_set)) {
-    $shortcut_set = shortcut_current_displayed_set();
-  }
+  $shortcut_set ??= shortcut_current_displayed_set();
 
   $cache_tags = [];
   foreach ($shortcut_set->getShortcuts() as $shortcut) {
diff --git a/core/modules/sqlite/src/Driver/Database/sqlite/Schema.php b/core/modules/sqlite/src/Driver/Database/sqlite/Schema.php
index 64bdffa8c8..e3a6cca480 100644
--- a/core/modules/sqlite/src/Driver/Database/sqlite/Schema.php
+++ b/core/modules/sqlite/src/Driver/Database/sqlite/Schema.php
@@ -122,9 +122,7 @@ protected function createKeySql($fields) {
    *   A field description array, as specified in the schema documentation.
    */
   protected function processField($field) {
-    if (!isset($field['size'])) {
-      $field['size'] = 'normal';
-    }
+    $field['size'] ??= 'normal';
 
     // Set the correct database-engine specific datatype.
     // In case one is already provided, force it to uppercase.
diff --git a/core/modules/system/src/PathBasedBreadcrumbBuilder.php b/core/modules/system/src/PathBasedBreadcrumbBuilder.php
index 64985ed1ed..2c0606b1ce 100644
--- a/core/modules/system/src/PathBasedBreadcrumbBuilder.php
+++ b/core/modules/system/src/PathBasedBreadcrumbBuilder.php
@@ -178,11 +178,9 @@ public function build(RouteMatchInterface $route_match) {
         $breadcrumb = $breadcrumb->addCacheableDependency($access);
         if ($access->isAllowed()) {
           $title = $this->titleResolver->getTitle($route_request, $route_match->getRouteObject());
-          if (!isset($title)) {
-            // Fallback to using the raw path component as the title if the
-            // route is missing a _title or _title_callback attribute.
-            $title = str_replace(['-', '_'], ' ', Unicode::ucfirst(end($path_elements)));
-          }
+          // Fallback to using the raw path component as the title if the
+          // route is missing a _title or _title_callback attribute.
+          $title ??= str_replace(['-', '_'], ' ', Unicode::ucfirst(end($path_elements)));
           $url = Url::fromRouteMatch($route_match);
           $links[] = new Link($title, $url);
         }
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 2de1283198..6441d1d919 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -743,13 +743,9 @@ function system_js_settings_alter(&$settings, AttachedAssetsInterface $assets) {
 
   // Only set core/drupalSettings values that haven't been set already.
   foreach ($path_settings as $key => $value) {
-    if (!isset($settings['path'][$key])) {
-      $settings['path'][$key] = $value;
-    }
-  }
-  if (!isset($settings['pluralDelimiter'])) {
-    $settings['pluralDelimiter'] = PoItem::DELIMITER;
+    $settings['path'][$key] ??= $value;
   }
+  $settings['pluralDelimiter'] ??= PoItem::DELIMITER;
   // Add the theme token to ajaxPageState, ensuring the database is available
   // before doing so. Also add the loaded libraries to ajaxPageState.
   /** @var \Drupal\Core\Asset\LibraryDependencyResolver $library_dependency_resolver */
diff --git a/core/modules/system/tests/src/Functional/Ajax/FrameworkTest.php b/core/modules/system/tests/src/Functional/Ajax/FrameworkTest.php
index afa6f8df54..846203694a 100644
--- a/core/modules/system/tests/src/Functional/Ajax/FrameworkTest.php
+++ b/core/modules/system/tests/src/Functional/Ajax/FrameworkTest.php
@@ -148,9 +148,7 @@ protected function assertCommand(array $haystack, array $needle): void {
    */
   protected function drupalGetAjax($path, array $options = [], array $headers = []) {
     $headers[] = 'X-Requested-With: XMLHttpRequest';
-    if (!isset($options['query'][MainContentViewSubscriber::WRAPPER_FORMAT])) {
-      $options['query'][MainContentViewSubscriber::WRAPPER_FORMAT] = 'drupal_ajax';
-    }
+    $options['query'][MainContentViewSubscriber::WRAPPER_FORMAT] ??= 'drupal_ajax';
     return Json::decode($this->drupalGet($path, $options, $headers));
   }
 
diff --git a/core/modules/system/tests/src/Functional/Pager/PagerTest.php b/core/modules/system/tests/src/Functional/Pager/PagerTest.php
index 9686d44dbb..b3551c4dc0 100644
--- a/core/modules/system/tests/src/Functional/Pager/PagerTest.php
+++ b/core/modules/system/tests/src/Functional/Pager/PagerTest.php
@@ -327,9 +327,7 @@ protected function assertPagerItems(int $current_page): void {
    * @internal
    */
   protected function assertClass(NodeElement $element, string $class, string $message = NULL): void {
-    if (!isset($message)) {
-      $message = "Class .$class found.";
-    }
+    $message ??= "Class .$class found.";
     $this->assertTrue($element->hasClass($class), $message);
   }
 
@@ -346,9 +344,7 @@ protected function assertClass(NodeElement $element, string $class, string $mess
    * @internal
    */
   protected function assertNoClass(NodeElement $element, string $class, string $message = NULL): void {
-    if (!isset($message)) {
-      $message = "Class .$class not found.";
-    }
+    $message ??= "Class .$class not found.";
     $this->assertFalse($element->hasClass($class), $message);
   }
 
diff --git a/core/modules/taxonomy/tests/src/Kernel/TermKernelTest.php b/core/modules/taxonomy/tests/src/Kernel/TermKernelTest.php
index b0b4d4f5dc..06beb124ee 100644
--- a/core/modules/taxonomy/tests/src/Kernel/TermKernelTest.php
+++ b/core/modules/taxonomy/tests/src/Kernel/TermKernelTest.php
@@ -119,9 +119,7 @@ public function testTaxonomyVocabularyTree() {
 
     // Count elements in every tree depth.
     foreach ($tree as $element) {
-      if (!isset($depth_count[$element->depth])) {
-        $depth_count[$element->depth] = 0;
-      }
+      $depth_count[$element->depth] ??= 0;
       $depth_count[$element->depth]++;
     }
     $this->assertEquals(3, $depth_count[0], 'Three elements in taxonomy tree depth 0.');
diff --git a/core/modules/text/text.module b/core/modules/text/text.module
index 5a6b85235d..e5a487e7bb 100644
--- a/core/modules/text/text.module
+++ b/core/modules/text/text.module
@@ -63,9 +63,7 @@ function text_help($route_name, RouteMatchInterface $route_match) {
  */
 function text_summary($text, $format = NULL, $size = NULL) {
 
-  if (!isset($size)) {
-    $size = \Drupal::config('text.settings')->get('default_summary_length');
-  }
+  $size ??= \Drupal::config('text.settings')->get('default_summary_length');
 
   // Find where the delimiter is in the body.
   $delimiter = strpos($text, '<!--break-->');
diff --git a/core/modules/toolbar/src/Element/ToolbarItem.php b/core/modules/toolbar/src/Element/ToolbarItem.php
index 2568b824b9..67b82e8b63 100644
--- a/core/modules/toolbar/src/Element/ToolbarItem.php
+++ b/core/modules/toolbar/src/Element/ToolbarItem.php
@@ -71,9 +71,7 @@ public static function preRenderToolbarItem($element) {
         'data-toolbar-tray' => $id . '-tray',
       ];
       // Merge in module-provided attributes.
-      if (!isset($element['tray']['#wrapper_attributes'])) {
-        $element['tray']['#wrapper_attributes'] = [];
-      }
+      $element['tray']['#wrapper_attributes'] ??= [];
       $element['tray']['#wrapper_attributes'] += $attributes;
       $element['tray']['#wrapper_attributes']['class'][] = 'toolbar-tray';
     }
diff --git a/core/modules/update/tests/src/Functional/UpdateSemverTestBase.php b/core/modules/update/tests/src/Functional/UpdateSemverTestBase.php
index 666c7d8977..f59fa2268b 100644
--- a/core/modules/update/tests/src/Functional/UpdateSemverTestBase.php
+++ b/core/modules/update/tests/src/Functional/UpdateSemverTestBase.php
@@ -53,9 +53,7 @@ protected function setUp(): void {
    * {@inheritdoc}
    */
   protected function refreshUpdateStatus($xml_map, $url = 'update-test') {
-    if (!isset($xml_map['drupal'])) {
-      $xml_map['drupal'] = '0.0';
-    }
+    $xml_map['drupal'] ??= '0.0';
     parent::refreshUpdateStatus($xml_map, $url);
   }
 
diff --git a/core/modules/update/update.authorize.inc b/core/modules/update/update.authorize.inc
index 742a3f159e..c4d0139ff4 100644
--- a/core/modules/update/update.authorize.inc
+++ b/core/modules/update/update.authorize.inc
@@ -131,16 +131,10 @@ function update_authorize_run_install($filetransfer, $project, $updater_name, $l
 function update_authorize_batch_copy_project($project, $updater_name, $local_url, $filetransfer, &$context) {
 
   // Initialize some variables in the Batch API $context array.
-  if (!isset($context['results']['log'])) {
-    $context['results']['log'] = [];
-  }
-  if (!isset($context['results']['log'][$project])) {
-    $context['results']['log'][$project] = [];
-  }
+  $context['results']['log'] ??= [];
+  $context['results']['log'][$project] ??= [];
 
-  if (!isset($context['results']['tasks'])) {
-    $context['results']['tasks'] = [];
-  }
+  $context['results']['tasks'] ??= [];
 
   // The batch API uses a session, and since all the arguments are serialized
   // and unserialized between requests, although the FileTransfer object itself
diff --git a/core/modules/update/update.compare.inc b/core/modules/update/update.compare.inc
index 466ca09f68..c028ae620f 100644
--- a/core/modules/update/update.compare.inc
+++ b/core/modules/update/update.compare.inc
@@ -316,10 +316,8 @@ function update_calculate_project_update_status(&$project_data, $available) {
         continue;
       }
     }
-    if (!isset($target_major)) {
-      // If there are no valid support branches, use the current major.
-      $target_major = $existing_major;
-    }
+    // If there are no valid support branches, use the current major.
+    $target_major ??= $existing_major;
 
   }
   else {
@@ -421,9 +419,7 @@ function update_calculate_project_update_status(&$project_data, $available) {
     // See if this is a higher major version than our target and yet still
     // supported. If so, record it as an "Also available" release.
     if ($release_major_version > $target_major) {
-      if (!isset($project_data['also'])) {
-        $project_data['also'] = [];
-      }
+      $project_data['also'] ??= [];
       if (!isset($project_data['also'][$release_major_version])) {
         $project_data['also'][$release_major_version] = $version;
         $project_data['releases'][$version] = $release_info;
diff --git a/core/modules/update/update.module b/core/modules/update/update.module
index 4d3337beaa..5bf3e85f38 100644
--- a/core/modules/update/update.module
+++ b/core/modules/update/update.module
@@ -604,9 +604,7 @@ function update_storage_clear() {
  */
 function _update_manager_unique_identifier() {
   static $id;
-  if (!isset($id)) {
-    $id = substr(hash('sha256', Settings::getHashSalt()), 0, 8);
-  }
+  $id ??= substr(hash('sha256', Settings::getHashSalt()), 0, 8);
   return $id;
 }
 
diff --git a/core/modules/update/update.report.inc b/core/modules/update/update.report.inc
index 8dbb17e094..893d17f5e0 100644
--- a/core/modules/update/update.report.inc
+++ b/core/modules/update/update.report.inc
@@ -50,12 +50,10 @@ function template_preprocess_update_report(&$variables) {
     ];
 
     // Build project rows.
-    if (!isset($rows[$project['project_type']])) {
-      $rows[$project['project_type']] = [
-        '#type' => 'table',
-        '#attributes' => ['class' => ['update']],
-      ];
-    }
+    $rows[$project['project_type']] ??= [
+      '#type' => 'table',
+      '#attributes' => ['class' => ['update']],
+    ];
     $row_key = !empty($project['title']) ? mb_strtolower($project['title']) : mb_strtolower($project['name']);
 
     // Add the project status row and details.
diff --git a/core/modules/user/src/PermissionHandler.php b/core/modules/user/src/PermissionHandler.php
index 50670b0381..4ffd698c08 100644
--- a/core/modules/user/src/PermissionHandler.php
+++ b/core/modules/user/src/PermissionHandler.php
@@ -105,9 +105,7 @@ public function __construct(ModuleHandlerInterface $module_handler, TranslationI
    *   The YAML discovery.
    */
   protected function getYamlDiscovery() {
-    if (!isset($this->yamlDiscovery)) {
-      $this->yamlDiscovery = new YamlDiscovery('permissions', $this->moduleHandler->getModuleDirectories());
-    }
+    $this->yamlDiscovery ??= new YamlDiscovery('permissions', $this->moduleHandler->getModuleDirectories());
     return $this->yamlDiscovery;
   }
 
diff --git a/core/modules/user/src/Plugin/migrate/process/UserLangcode.php b/core/modules/user/src/Plugin/migrate/process/UserLangcode.php
index 174c8a557c..0f02a49bf8 100644
--- a/core/modules/user/src/Plugin/migrate/process/UserLangcode.php
+++ b/core/modules/user/src/Plugin/migrate/process/UserLangcode.php
@@ -58,9 +58,7 @@ public static function create(ContainerInterface $container, array $configuratio
    * {@inheritdoc}
    */
   public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
-    if (!isset($this->configuration['fallback_to_site_default'])) {
-      $this->configuration['fallback_to_site_default'] = TRUE;
-    }
+    $this->configuration['fallback_to_site_default'] ??= TRUE;
 
     // If the user's language is empty, it means the locale module was not
     // installed, so the user's langcode should be English and the user's
diff --git a/core/modules/user/src/Plugin/migrate/process/d6/UserUpdate7002.php b/core/modules/user/src/Plugin/migrate/process/d6/UserUpdate7002.php
index 84f6dfecc2..2ee9545801 100644
--- a/core/modules/user/src/Plugin/migrate/process/d6/UserUpdate7002.php
+++ b/core/modules/user/src/Plugin/migrate/process/d6/UserUpdate7002.php
@@ -39,9 +39,7 @@ class UserUpdate7002 extends ProcessPluginBase implements ContainerFactoryPlugin
   public function __construct(array $configuration, $plugin_id, array $plugin_definition, Config $date_config) {
     parent::__construct($configuration, $plugin_id, $plugin_definition);
     $this->dateConfig = $date_config;
-    if (!isset(static::$timezones)) {
-      static::$timezones = TimeZoneFormHelper::getOptionsList();
-    }
+    static::$timezones ??= TimeZoneFormHelper::getOptionsList();
   }
 
   /**
diff --git a/core/modules/user/tests/src/Traits/UserCreationTrait.php b/core/modules/user/tests/src/Traits/UserCreationTrait.php
index 510d722ebd..35ec3e0aba 100644
--- a/core/modules/user/tests/src/Traits/UserCreationTrait.php
+++ b/core/modules/user/tests/src/Traits/UserCreationTrait.php
@@ -239,15 +239,11 @@ protected function createAdminRole($rid = NULL, $name = NULL, $weight = NULL) {
    */
   protected function createRole(array $permissions, $rid = NULL, $name = NULL, $weight = NULL) {
     // Generate a random, lowercase machine name if none was passed.
-    if (!isset($rid)) {
-      $rid = $this->randomMachineName(8);
-    }
+    $rid ??= $this->randomMachineName(8);
     // Generate a random label.
-    if (!isset($name)) {
-      // In the role UI role names are trimmed and random string can start or
-      // end with a space.
-      $name = trim($this->randomString(8));
-    }
+    // In the role UI role names are trimmed and random string can start or
+    // end with a space.
+    $name ??= trim($this->randomString(8));
 
     // Check the all the permissions strings are valid.
     if (!$this->checkPermissions($permissions)) {
diff --git a/core/modules/views/src/Entity/Render/EntityFieldRenderer.php b/core/modules/views/src/Entity/Render/EntityFieldRenderer.php
index 5074969ab7..fb994be8da 100644
--- a/core/modules/views/src/Entity/Render/EntityFieldRenderer.php
+++ b/core/modules/views/src/Entity/Render/EntityFieldRenderer.php
@@ -139,9 +139,7 @@ public function render(ResultRow $row, EntityField $field = NULL) {
     // The method is called for each field in each result row. In order to
     // leverage multiple-entity building of formatter output, we build the
     // render arrays for all fields in all rows on the first call.
-    if (!isset($this->build)) {
-      $this->build = $this->buildFields($this->view->result);
-    }
+    $this->build ??= $this->buildFields($this->view->result);
 
     if (isset($field)) {
       $field_id = $field->options['id'];
diff --git a/core/modules/views/src/Entity/View.php b/core/modules/views/src/Entity/View.php
index 8fb42eadf4..2c30035b65 100644
--- a/core/modules/views/src/Entity/View.php
+++ b/core/modules/views/src/Entity/View.php
@@ -119,9 +119,7 @@ class View extends ConfigEntityBase implements ViewEntityInterface {
    */
   public function getExecutable() {
     // Ensure that an executable View is available.
-    if (!isset($this->executable)) {
-      $this->executable = Views::executableFactory()->get($this);
-    }
+    $this->executable ??= Views::executableFactory()->get($this);
 
     return $this->executable;
   }
diff --git a/core/modules/views/src/EntityViewsData.php b/core/modules/views/src/EntityViewsData.php
index eb964521af..027f82c4a8 100644
--- a/core/modules/views/src/EntityViewsData.php
+++ b/core/modules/views/src/EntityViewsData.php
@@ -118,9 +118,7 @@ public static function createInstance(ContainerInterface $container, EntityTypeI
    * @return \Drupal\Core\Field\FieldStorageDefinitionInterface[]
    */
   protected function getFieldStorageDefinitions() {
-    if (!isset($this->fieldStorageDefinitions)) {
-      $this->fieldStorageDefinitions = $this->entityFieldManager->getFieldStorageDefinitions($this->entityType->id());
-    }
+    $this->fieldStorageDefinitions ??= $this->entityFieldManager->getFieldStorageDefinitions($this->entityType->id());
     return $this->fieldStorageDefinitions;
   }
 
diff --git a/core/modules/views/src/FieldAPIHandlerTrait.php b/core/modules/views/src/FieldAPIHandlerTrait.php
index b3ec833a52..a1f51e51a6 100644
--- a/core/modules/views/src/FieldAPIHandlerTrait.php
+++ b/core/modules/views/src/FieldAPIHandlerTrait.php
@@ -72,9 +72,7 @@ protected function getFieldStorageDefinition() {
    *   The entity field manager.
    */
   protected function getEntityFieldManager() {
-    if (!isset($this->entityFieldManager)) {
-      $this->entityFieldManager = \Drupal::service('entity_field.manager');
-    }
+    $this->entityFieldManager ??= \Drupal::service('entity_field.manager');
     return $this->entityFieldManager;
   }
 
diff --git a/core/modules/views/src/Plugin/views/HandlerBase.php b/core/modules/views/src/Plugin/views/HandlerBase.php
index ad7ee244e3..ec782f2a8c 100644
--- a/core/modules/views/src/Plugin/views/HandlerBase.php
+++ b/core/modules/views/src/Plugin/views/HandlerBase.php
@@ -134,9 +134,7 @@ public function init(ViewExecutable $view, DisplayPluginBase $display, array &$o
 
     if (isset($options['field'])) {
       $this->field = $options['field'];
-      if (!isset($this->realField)) {
-        $this->realField = $options['field'];
-      }
+      $this->realField ??= $options['field'];
     }
 
     $this->query = &$view->query;
@@ -547,9 +545,7 @@ public function setRelationship() {
    * {@inheritdoc}
    */
   public function ensureMyTable() {
-    if (!isset($this->tableAlias)) {
-      $this->tableAlias = $this->query->ensureTable($this->table, $this->relationship);
-    }
+    $this->tableAlias ??= $this->query->ensureTable($this->table, $this->relationship);
     return $this->tableAlias;
   }
 
diff --git a/core/modules/views/src/Plugin/views/PluginBase.php b/core/modules/views/src/Plugin/views/PluginBase.php
index e478e91301..cca876d938 100644
--- a/core/modules/views/src/Plugin/views/PluginBase.php
+++ b/core/modules/views/src/Plugin/views/PluginBase.php
@@ -226,9 +226,7 @@ public function unpackOptions(&$storage, $options, $definition = NULL, $all = TR
       return;
     }
 
-    if (!isset($definition)) {
-      $definition = $this->defineOptions();
-    }
+    $definition ??= $this->defineOptions();
 
     foreach ($options as $key => $value) {
       if (is_array($value)) {
@@ -394,9 +392,7 @@ protected function viewsTokenReplace($text, $tokens) {
           assert(is_numeric($key) || preg_match('/^[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*$/', $key) === 1, 'Tokens need to be valid Twig variables.');
           $token_array = [$key => $token_array];
         }
-        if (!isset($twig_tokens[$top])) {
-          $twig_tokens[$top] = [];
-        }
+        $twig_tokens[$top] ??= [];
         $twig_tokens[$top] += $token_array;
       }
     }
@@ -660,9 +656,7 @@ public static function queryLanguageSubstitutions() {
    * @return \Drupal\Core\Render\RendererInterface
    */
   protected function getRenderer() {
-    if (!isset($this->renderer)) {
-      $this->renderer = \Drupal::service('renderer');
-    }
+    $this->renderer ??= \Drupal::service('renderer');
 
     return $this->renderer;
   }
diff --git a/core/modules/views/src/Plugin/views/argument/ArgumentPluginBase.php b/core/modules/views/src/Plugin/views/argument/ArgumentPluginBase.php
index bbc33b438b..7f6009f1b8 100644
--- a/core/modules/views/src/Plugin/views/argument/ArgumentPluginBase.php
+++ b/core/modules/views/src/Plugin/views/argument/ArgumentPluginBase.php
@@ -137,9 +137,7 @@ public function init(ViewExecutable $view, DisplayPluginBase $display, array &$o
   }
 
   public function isException($arg = NULL) {
-    if (!isset($arg)) {
-      $arg = $this->argument ?? NULL;
-    }
+    $arg ??= $this->argument ?? NULL;
     return !empty($this->options['exception']['value']) && $this->options['exception']['value'] === $arg;
   }
 
@@ -751,9 +749,7 @@ public function defaultSummaryForm(&$form, FormStateInterface $form_state) {
    *   building the view will be aborted here.
    */
   public function defaultAction($info = NULL) {
-    if (!isset($info)) {
-      $info = $this->defaultActions($this->options['default_action']);
-    }
+    $info ??= $this->defaultActions($this->options['default_action']);
 
     if (!$info) {
       return FALSE;
diff --git a/core/modules/views/src/Plugin/views/display/Attachment.php b/core/modules/views/src/Plugin/views/display/Attachment.php
index e6e73fbd8a..44d261f34a 100644
--- a/core/modules/views/src/Plugin/views/display/Attachment.php
+++ b/core/modules/views/src/Plugin/views/display/Attachment.php
@@ -90,9 +90,7 @@ public function optionsSummary(&$categories, &$options) {
       }
     }
 
-    if (!isset($attach_to)) {
-      $attach_to = $this->t('Not defined');
-    }
+    $attach_to ??= $this->t('Not defined');
 
     $options['displays'] = [
       'category' => 'attachment',
diff --git a/core/modules/views/src/Plugin/views/display/DisplayPluginBase.php b/core/modules/views/src/Plugin/views/display/DisplayPluginBase.php
index 81c37a2c37..03346f9a48 100644
--- a/core/modules/views/src/Plugin/views/display/DisplayPluginBase.php
+++ b/core/modules/views/src/Plugin/views/display/DisplayPluginBase.php
@@ -2061,9 +2061,7 @@ public function setOverride($section, $new_state = NULL) {
       return;
     }
 
-    if (!isset($new_state)) {
-      $new_state = empty($this->options['defaults'][$section]);
-    }
+    $new_state ??= empty($this->options['defaults'][$section]);
 
     // For each option that is part of this group, fix our settings.
     foreach ($options as $option) {
@@ -2299,9 +2297,7 @@ public function renderArea($area, $empty = FALSE) {
    * {@inheritdoc}
    */
   public function access(AccountInterface $account = NULL) {
-    if (!isset($account)) {
-      $account = \Drupal::currentUser();
-    }
+    $account ??= \Drupal::currentUser();
 
     $plugin = $this->getPlugin('access');
     /** @var \Drupal\views\Plugin\views\access\AccessPluginBase $plugin */
diff --git a/core/modules/views/src/Plugin/views/display/Feed.php b/core/modules/views/src/Plugin/views/display/Feed.php
index caf6f8cbc9..300416be4e 100644
--- a/core/modules/views/src/Plugin/views/display/Feed.php
+++ b/core/modules/views/src/Plugin/views/display/Feed.php
@@ -284,9 +284,7 @@ public function optionsSummary(&$categories, &$options) {
       }
     }
 
-    if (!isset($attach_to)) {
-      $attach_to = $this->t('None');
-    }
+    $attach_to ??= $this->t('None');
 
     $options['displays'] = [
       'category' => 'page',
diff --git a/core/modules/views/src/Plugin/views/display/PathPluginBase.php b/core/modules/views/src/Plugin/views/display/PathPluginBase.php
index 984d740e57..f53cfae4d1 100644
--- a/core/modules/views/src/Plugin/views/display/PathPluginBase.php
+++ b/core/modules/views/src/Plugin/views/display/PathPluginBase.php
@@ -195,10 +195,8 @@ protected function getRoute($view_id, $display_id) {
 
     // Add access check parameters to the route.
     $access_plugin = $this->getPlugin('access');
-    if (!isset($access_plugin)) {
-      // @todo Do we want to support a default plugin in getPlugin itself?
-      $access_plugin = Views::pluginManager('access')->createInstance('none');
-    }
+    // @todo Do we want to support a default plugin in getPlugin itself?
+    $access_plugin ??= Views::pluginManager('access')->createInstance('none');
     $access_plugin->alterRouteDefinition($route);
 
     // Set the argument map, in order to support named parameters.
diff --git a/core/modules/views/src/Plugin/views/field/EntityField.php b/core/modules/views/src/Plugin/views/field/EntityField.php
index 6ef6b011b8..71a2fa0f78 100644
--- a/core/modules/views/src/Plugin/views/field/EntityField.php
+++ b/core/modules/views/src/Plugin/views/field/EntityField.php
@@ -547,9 +547,7 @@ public function submitFormCalculateOptions(array $options, array $form_state_opt
     // conflict.
     unset($options['settings']);
     $options = $form_state_options + $options;
-    if (!isset($options['settings'])) {
-      $options['settings'] = [];
-    }
+    $options['settings'] ??= [];
     return $options;
   }
 
@@ -1017,9 +1015,7 @@ protected function addSelfTokens(&$tokens, $item) {
    *   The field formatter instance.
    */
   protected function getFormatterInstance($format = NULL) {
-    if (!isset($format)) {
-      $format = $this->options['type'];
-    }
+    $format ??= $this->options['type'];
     $settings = $this->options['settings'] + $this->formatterPluginManager->getDefaultSettings($format);
 
     $options = [
diff --git a/core/modules/views/src/Plugin/views/field/EntityOperations.php b/core/modules/views/src/Plugin/views/field/EntityOperations.php
index f8e36f9f0f..28afdba973 100644
--- a/core/modules/views/src/Plugin/views/field/EntityOperations.php
+++ b/core/modules/views/src/Plugin/views/field/EntityOperations.php
@@ -138,9 +138,7 @@ public function render(ResultRow $values) {
     $operations = $this->entityTypeManager->getListBuilder($entity->getEntityTypeId())->getOperations($entity);
     if ($this->options['destination']) {
       foreach ($operations as &$operation) {
-        if (!isset($operation['query'])) {
-          $operation['query'] = [];
-        }
+        $operation['query'] ??= [];
         $operation['query'] += $this->getDestinationArray();
       }
     }
diff --git a/core/modules/views/src/Plugin/views/field/FieldPluginBase.php b/core/modules/views/src/Plugin/views/field/FieldPluginBase.php
index 412da1b2d4..ac0a24b807 100644
--- a/core/modules/views/src/Plugin/views/field/FieldPluginBase.php
+++ b/core/modules/views/src/Plugin/views/field/FieldPluginBase.php
@@ -140,9 +140,7 @@ public function init(ViewExecutable $view, DisplayPluginBase $display, array &$o
       $this->additional_fields = $this->definition['additional fields'];
     }
 
-    if (!isset($this->options['exclude'])) {
-      $this->options['exclude'] = '';
-    }
+    $this->options['exclude'] ??= '';
   }
 
   /**
@@ -1369,9 +1367,7 @@ public function renderText($alter) {
     $this->last_render_text = $value;
 
     if (!empty($alter['make_link']) && (!empty($alter['path']) || !empty($alter['url']))) {
-      if (!isset($tokens)) {
-        $tokens = $this->getRenderTokens($alter);
-      }
+      $tokens ??= $this->getRenderTokens($alter);
       $value = $this->renderAsLink($alter, $value, $tokens);
     }
 
@@ -1569,9 +1565,7 @@ protected function renderAsLink($alter, $text, $tokens) {
     // currently can only be altered in preprocessors and not within the UI.
     if (isset($alter['link_attributes']) && is_array($alter['link_attributes'])) {
       foreach ($alter['link_attributes'] as $key => $attribute) {
-        if (!isset($options['attributes'][$key])) {
-          $options['attributes'][$key] = $this->viewsTokenReplace($attribute, $tokens);
-        }
+        $options['attributes'][$key] ??= $this->viewsTokenReplace($attribute, $tokens);
       }
     }
 
@@ -1638,9 +1632,7 @@ public function getRenderTokens($item) {
     $count = 0;
     foreach ($this->displayHandler->getHandlers('argument') as $arg => $handler) {
       $token = "{{ arguments.$arg }}";
-      if (!isset($tokens[$token])) {
-        $tokens[$token] = '';
-      }
+      $tokens[$token] ??= '';
 
       // Use strip tags as there should never be HTML in the path.
       // However, we need to preserve special characters like " that
@@ -1878,9 +1870,7 @@ public static function trimText($alter, $value) {
    * @return \Drupal\Core\Utility\LinkGeneratorInterface
    */
   protected function linkGenerator() {
-    if (!isset($this->linkGenerator)) {
-      $this->linkGenerator = \Drupal::linkGenerator();
-    }
+    $this->linkGenerator ??= \Drupal::linkGenerator();
     return $this->linkGenerator;
   }
 
@@ -1890,9 +1880,7 @@ protected function linkGenerator() {
    * @return \Drupal\Core\Render\RendererInterface
    */
   protected function getRenderer() {
-    if (!isset($this->renderer)) {
-      $this->renderer = \Drupal::service('renderer');
-    }
+    $this->renderer ??= \Drupal::service('renderer');
 
     return $this->renderer;
   }
diff --git a/core/modules/views/src/Plugin/views/filter/BooleanOperator.php b/core/modules/views/src/Plugin/views/filter/BooleanOperator.php
index 81c2f47aa8..f63b395797 100644
--- a/core/modules/views/src/Plugin/views/filter/BooleanOperator.php
+++ b/core/modules/views/src/Plugin/views/filter/BooleanOperator.php
@@ -150,9 +150,7 @@ public function getValueOptions() {
     }
 
     // Provide a fallback if the above didn't set anything.
-    if (!isset($this->valueOptions)) {
-      $this->valueOptions = [1 => $this->t('True'), 0 => $this->t('False')];
-    }
+    $this->valueOptions ??= [1 => $this->t('True'), 0 => $this->t('False')];
   }
 
   protected function defineOptions() {
diff --git a/core/modules/views/src/Plugin/views/filter/FilterPluginBase.php b/core/modules/views/src/Plugin/views/filter/FilterPluginBase.php
index 1d24826b75..7ee1a8565e 100644
--- a/core/modules/views/src/Plugin/views/filter/FilterPluginBase.php
+++ b/core/modules/views/src/Plugin/views/filter/FilterPluginBase.php
@@ -1461,9 +1461,7 @@ public function storeGroupInput($input, $status) {
     }
 
     if ($status !== FALSE) {
-      if (!isset($views_session[$this->view->storage->id()][$display_id])) {
-        $views_session[$this->view->storage->id()][$display_id] = [];
-      }
+      $views_session[$this->view->storage->id()][$display_id] ??= [];
       $views_session[$this->view->storage->id()][$display_id][$this->options['group_info']['identifier']] = $input[$this->options['group_info']['identifier']];
     }
     if (!empty($views_session)) {
@@ -1574,9 +1572,7 @@ public function storeExposedInput($input, $status) {
     }
 
     if ($status) {
-      if (!isset($views_session[$this->view->storage->id()][$display_id])) {
-        $views_session[$this->view->storage->id()][$display_id] = [];
-      }
+      $views_session[$this->view->storage->id()][$display_id] ??= [];
 
       $session_ref = &$views_session[$this->view->storage->id()][$display_id];
 
diff --git a/core/modules/views/src/Plugin/views/filter/InOperator.php b/core/modules/views/src/Plugin/views/filter/InOperator.php
index 52c198ce05..1bb28cdcce 100644
--- a/core/modules/views/src/Plugin/views/filter/InOperator.php
+++ b/core/modules/views/src/Plugin/views/filter/InOperator.php
@@ -263,9 +263,7 @@ protected function valueForm(&$form, FormStateInterface $form_state) {
    * When using exposed filters, we may be required to reduce the set.
    */
   public function reduceValueOptions($input = NULL) {
-    if (!isset($input)) {
-      $input = $this->valueOptions;
-    }
+    $input ??= $this->valueOptions;
 
     // Because options may be an array of strings, or an array of mixed arrays
     // and strings (optgroups), or an array of objects, or a form of Markup, we
diff --git a/core/modules/views/src/Plugin/views/filter/NumericFilter.php b/core/modules/views/src/Plugin/views/filter/NumericFilter.php
index 2e34e069cf..6948b87f14 100644
--- a/core/modules/views/src/Plugin/views/filter/NumericFilter.php
+++ b/core/modules/views/src/Plugin/views/filter/NumericFilter.php
@@ -317,13 +317,11 @@ protected function valueForm(&$form, FormStateInterface $form_state) {
         $user_input[$identifier]['max'] = $this->value['max'];
       }
 
-      if (!isset($form['value'])) {
-        // Ensure there is something in the 'value'.
-        $form['value'] = [
-          '#type' => 'value',
-          '#value' => NULL,
-        ];
-      }
+      // Ensure there is something in the 'value'.
+      $form['value'] ??= [
+        '#type' => 'value',
+        '#value' => NULL,
+      ];
     }
   }
 
diff --git a/core/modules/views/src/Plugin/views/filter/StringFilter.php b/core/modules/views/src/Plugin/views/filter/StringFilter.php
index ba8fe2cf99..3bd8c316cd 100644
--- a/core/modules/views/src/Plugin/views/filter/StringFilter.php
+++ b/core/modules/views/src/Plugin/views/filter/StringFilter.php
@@ -303,13 +303,11 @@ protected function valueForm(&$form, FormStateInterface $form_state) {
       }
     }
 
-    if (!isset($form['value'])) {
-      // Ensure there is something in the 'value'.
-      $form['value'] = [
-        '#type' => 'value',
-        '#value' => NULL,
-      ];
-    }
+    // Ensure there is something in the 'value'.
+    $form['value'] ??= [
+      '#type' => 'value',
+      '#value' => NULL,
+    ];
   }
 
   /**
diff --git a/core/modules/views/src/Plugin/views/query/QueryPluginBase.php b/core/modules/views/src/Plugin/views/query/QueryPluginBase.php
index 446b636f37..fd38fee12f 100644
--- a/core/modules/views/src/Plugin/views/query/QueryPluginBase.php
+++ b/core/modules/views/src/Plugin/views/query/QueryPluginBase.php
@@ -177,9 +177,7 @@ public function setWhereGroup($type = 'AND', $group = NULL, $where = 'where') {
     // Set an alias.
     $groups = &$this->$where;
 
-    if (!isset($group)) {
-      $group = empty($groups) ? 1 : max(array_keys($groups)) + 1;
-    }
+    $group ??= empty($groups) ? 1 : max(array_keys($groups)) + 1;
 
     // Create an empty group
     if (empty($groups[$group])) {
diff --git a/core/modules/views/src/Plugin/views/query/Sql.php b/core/modules/views/src/Plugin/views/query/Sql.php
index af57e33ec4..f7f5717b8a 100644
--- a/core/modules/views/src/Plugin/views/query/Sql.php
+++ b/core/modules/views/src/Plugin/views/query/Sql.php
@@ -518,9 +518,7 @@ public function queueTable($table, $relationship = NULL, JoinPluginBase $join =
     $alias = $this->markTable($table, $relationship, $alias);
 
     // If no alias is specified, give it the default.
-    if (!isset($alias)) {
-      $alias = $this->tables[$relationship][$table]['alias'] . $this->tables[$relationship][$table]['count'];
-    }
+    $alias ??= $this->tables[$relationship][$table]['alias'] . $this->tables[$relationship][$table]['count'];
 
     // If this is a relationship based table, add a marker with
     // the relationship as a primary table for the alias.
@@ -616,9 +614,7 @@ public function ensureTable($table, $relationship = NULL, JoinPluginBase $join =
     }
 
     // If we do not have join info, fetch it.
-    if (!isset($join)) {
-      $join = $this->getJoinData($table, $this->relationships[$relationship]['base']);
-    }
+    $join ??= $this->getJoinData($table, $this->relationships[$relationship]['base']);
 
     // If it can't be fetched, this won't work.
     if (empty($join)) {
@@ -673,18 +669,14 @@ public function ensureTable($table, $relationship = NULL, JoinPluginBase $join =
    * additional copies will NOT be added if the table is already there.
    */
   protected function ensurePath($table, $relationship = NULL, $join = NULL, $traced = [], $add = []) {
-    if (!isset($relationship)) {
-      $relationship = $this->view->storage->get('base_table');
-    }
+    $relationship ??= $this->view->storage->get('base_table');
 
     if (!array_key_exists($relationship, $this->relationships)) {
       return FALSE;
     }
 
     // If we do not have join info, fetch it.
-    if (!isset($join)) {
-      $join = $this->getJoinData($table, $this->relationships[$relationship]['base']);
-    }
+    $join ??= $this->getJoinData($table, $this->relationships[$relationship]['base']);
 
     // If it can't be fetched, this won't work.
     if (empty($join)) {
@@ -1321,9 +1313,7 @@ public function query($get_count = FALSE) {
     else {
       $this->getCountOptimized = FALSE;
     }
-    if (!isset($this->getCountOptimized)) {
-      $this->getCountOptimized = TRUE;
-    }
+    $this->getCountOptimized ??= TRUE;
 
     // Go ahead and build the query.
     $query = $this->getConnection()
@@ -1592,9 +1582,7 @@ public function loadEntities(&$results) {
     $entity_types = [];
     foreach ($entity_information as $info) {
       $entity_type = $info['entity_type'];
-      if (!isset($entity_types[$entity_type])) {
-        $entity_types[$entity_type] = $this->entityTypeManager->getDefinition($entity_type);
-      }
+      $entity_types[$entity_type] ??= $this->entityTypeManager->getDefinition($entity_type);
     }
 
     // Assemble a list of entities to load.
diff --git a/core/modules/views/src/Plugin/views/row/RssFields.php b/core/modules/views/src/Plugin/views/row/RssFields.php
index 924cd7b6e2..a954cce1a7 100644
--- a/core/modules/views/src/Plugin/views/row/RssFields.php
+++ b/core/modules/views/src/Plugin/views/row/RssFields.php
@@ -123,9 +123,7 @@ public function validate() {
 
   public function render($row) {
     static $row_index;
-    if (!isset($row_index)) {
-      $row_index = 0;
-    }
+    $row_index ??= 0;
 
     // Create the RSS item object.
     $item = new \stdClass();
diff --git a/core/modules/views/src/ViewExecutable.php b/core/modules/views/src/ViewExecutable.php
index 7b04186dbe..1f55e12da7 100644
--- a/core/modules/views/src/ViewExecutable.php
+++ b/core/modules/views/src/ViewExecutable.php
@@ -1505,10 +1505,8 @@ public function render($display_id = NULL) {
     // Initialize the style plugin.
     $this->initStyle();
 
-    if (!isset($this->response)) {
-      // Set the response so other parts can alter it.
-      $this->response = new Response('', 200);
-    }
+    // Set the response so other parts can alter it.
+    $this->response ??= new Response('', 200);
 
     // Give field handlers the opportunity to perform additional queries
     // using the entire resultset prior to rendering.
@@ -1804,9 +1802,7 @@ public function setResponse(Response $response) {
    *   The response object of the view.
    */
   public function getResponse() {
-    if (!isset($this->response)) {
-      $this->response = new Response();
-    }
+    $this->response ??= new Response();
     return $this->response;
   }
 
@@ -2267,9 +2263,7 @@ public function getHandlers($type, $display_id = NULL) {
 
     $this->setDisplay($display_id);
 
-    if (!isset($display_id)) {
-      $display_id = $this->current_display;
-    }
+    $display_id ??= $this->current_display;
 
     // Get info about the types so we can get the right data.
     $types = static::getHandlerTypes();
diff --git a/core/modules/views/src/Views.php b/core/modules/views/src/Views.php
index 2373ebbc21..494accf29e 100644
--- a/core/modules/views/src/Views.php
+++ b/core/modules/views/src/Views.php
@@ -394,14 +394,12 @@ public static function pluginList() {
           // Key first by the plugin type, then the name.
           $key = $type . ':' . $name;
           // Add info for this plugin.
-          if (!isset($plugins[$key])) {
-            $plugins[$key] = [
-              'type' => $type,
-              'title' => $info[$name]['title'],
-              'provider' => $info[$name]['provider'],
-              'views' => [],
-            ];
-          }
+          $plugins[$key] ??= [
+            'type' => $type,
+            'title' => $info[$name]['title'],
+            'provider' => $info[$name]['provider'],
+            'views' => [],
+          ];
 
           // Add this view to the list for this plugin.
           $plugins[$key]['views'][$view->id()] = $view->id();
@@ -429,73 +427,71 @@ public static function pluginList() {
   public static function getHandlerTypes() {
     // Statically cache this so translation only occurs once per request for all
     // of these values.
-    if (!isset(static::$handlerTypes)) {
-      static::$handlerTypes = [
-        'field' => [
-          // title
-          'title' => static::t('Fields'),
-          // Lowercase title for mid-sentence.
-          'ltitle' => static::t('fields'),
-          // Singular title.
-          'stitle' => static::t('Field'),
-          // Singular lowercase title for mid sentence
-          'lstitle' => static::t('field'),
-          'plural' => 'fields',
-        ],
-        'argument' => [
-          'title' => static::t('Contextual filters'),
-          'ltitle' => static::t('contextual filters'),
-          'stitle' => static::t('Contextual filter'),
-          'lstitle' => static::t('contextual filter'),
-          'plural' => 'arguments',
-        ],
-        'sort' => [
-          'title' => static::t('Sort criteria'),
-          'ltitle' => static::t('sort criteria'),
-          'stitle' => static::t('Sort criterion'),
-          'lstitle' => static::t('sort criterion'),
-          'plural' => 'sorts',
-        ],
-        'filter' => [
-          'title' => static::t('Filter criteria'),
-          'ltitle' => static::t('filter criteria'),
-          'stitle' => static::t('Filter criterion'),
-          'lstitle' => static::t('filter criterion'),
-          'plural' => 'filters',
-        ],
-        'relationship' => [
-          'title' => static::t('Relationships'),
-          'ltitle' => static::t('relationships'),
-          'stitle' => static::t('Relationship'),
-          'lstitle' => static::t('Relationship'),
-          'plural' => 'relationships',
-        ],
-        'header' => [
-          'title' => static::t('Header'),
-          'ltitle' => static::t('header'),
-          'stitle' => static::t('Header'),
-          'lstitle' => static::t('Header'),
-          'plural' => 'header',
-          'type' => 'area',
-        ],
-        'footer' => [
-          'title' => static::t('Footer'),
-          'ltitle' => static::t('footer'),
-          'stitle' => static::t('Footer'),
-          'lstitle' => static::t('Footer'),
-          'plural' => 'footer',
-          'type' => 'area',
-        ],
-        'empty' => [
-          'title' => static::t('No results behavior'),
-          'ltitle' => static::t('no results behavior'),
-          'stitle' => static::t('No results behavior'),
-          'lstitle' => static::t('No results behavior'),
-          'plural' => 'empty',
-          'type' => 'area',
-        ],
-      ];
-    }
+    static::$handlerTypes ??= [
+      'field' => [
+        // title
+        'title' => static::t('Fields'),
+        // Lowercase title for mid-sentence.
+        'ltitle' => static::t('fields'),
+        // Singular title.
+        'stitle' => static::t('Field'),
+        // Singular lowercase title for mid sentence
+        'lstitle' => static::t('field'),
+        'plural' => 'fields',
+      ],
+      'argument' => [
+        'title' => static::t('Contextual filters'),
+        'ltitle' => static::t('contextual filters'),
+        'stitle' => static::t('Contextual filter'),
+        'lstitle' => static::t('contextual filter'),
+        'plural' => 'arguments',
+      ],
+      'sort' => [
+        'title' => static::t('Sort criteria'),
+        'ltitle' => static::t('sort criteria'),
+        'stitle' => static::t('Sort criterion'),
+        'lstitle' => static::t('sort criterion'),
+        'plural' => 'sorts',
+      ],
+      'filter' => [
+        'title' => static::t('Filter criteria'),
+        'ltitle' => static::t('filter criteria'),
+        'stitle' => static::t('Filter criterion'),
+        'lstitle' => static::t('filter criterion'),
+        'plural' => 'filters',
+      ],
+      'relationship' => [
+        'title' => static::t('Relationships'),
+        'ltitle' => static::t('relationships'),
+        'stitle' => static::t('Relationship'),
+        'lstitle' => static::t('Relationship'),
+        'plural' => 'relationships',
+      ],
+      'header' => [
+        'title' => static::t('Header'),
+        'ltitle' => static::t('header'),
+        'stitle' => static::t('Header'),
+        'lstitle' => static::t('Header'),
+        'plural' => 'header',
+        'type' => 'area',
+      ],
+      'footer' => [
+        'title' => static::t('Footer'),
+        'ltitle' => static::t('footer'),
+        'stitle' => static::t('Footer'),
+        'lstitle' => static::t('Footer'),
+        'plural' => 'footer',
+        'type' => 'area',
+      ],
+      'empty' => [
+        'title' => static::t('No results behavior'),
+        'ltitle' => static::t('no results behavior'),
+        'stitle' => static::t('No results behavior'),
+        'lstitle' => static::t('No results behavior'),
+        'plural' => 'empty',
+        'type' => 'area',
+      ],
+    ];
 
     return static::$handlerTypes;
   }
diff --git a/core/modules/views/views.module b/core/modules/views/views.module
index 0735b1de87..c728f91bb9 100644
--- a/core/modules/views/views.module
+++ b/core/modules/views/views.module
@@ -184,9 +184,7 @@ function views_theme($existing, $type, $theme, $path) {
 
       // For the views module we ensure views.theme.inc is included.
       if ($def['provider'] == 'views') {
-        if (!isset($hooks[$def['theme']]['includes'])) {
-          $hooks[$def['theme']]['includes'] = [];
-        }
+        $hooks[$def['theme']]['includes'] ??= [];
         if (!in_array('views.theme.inc', $hooks[$def['theme']]['includes'])) {
           $hooks[$def['theme']]['includes'][] = $module_dir . '/views.theme.inc';
         }
@@ -364,9 +362,7 @@ function views_theme_suggestions_container_alter(array &$suggestions, array $var
  * @see template_preprocess_views_view()
  */
 function views_add_contextual_links(&$render_element, $location, $display_id, array $view_element = NULL) {
-  if (!isset($view_element)) {
-    $view_element = $render_element;
-  }
+  $view_element ??= $render_element;
   $view_element['#cache_properties'] = ['view_id', 'view_display_show_admin_links', 'view_display_plugin_id'];
   $view_id = $view_element['#view_id'];
   $show_admin_links = $view_element['#view_display_show_admin_links'];
diff --git a/core/modules/views/views.theme.inc b/core/modules/views/views.theme.inc
index 58d34f16ae..5617efb5ce 100644
--- a/core/modules/views/views.theme.inc
+++ b/core/modules/views/views.theme.inc
@@ -585,9 +585,7 @@ function template_preprocess_views_view_table(&$variables) {
       if (!empty($fields[$field])) {
         $field_output = $handler->getField($num, $field);
         $column_reference['wrapper_element'] = $fields[$field]->elementType(TRUE, TRUE);
-        if (!isset($column_reference['content'])) {
-          $column_reference['content'] = [];
-        }
+        $column_reference['content'] ??= [];
 
         // Only bother with separators and stuff if the field shows up.
         // Place the field into the column, along with an optional separator.
diff --git a/core/modules/views_ui/src/ProxyClass/ParamConverter/ViewUIConverter.php b/core/modules/views_ui/src/ProxyClass/ParamConverter/ViewUIConverter.php
index 9ef21bfa96..644a01dd22 100644
--- a/core/modules/views_ui/src/ProxyClass/ParamConverter/ViewUIConverter.php
+++ b/core/modules/views_ui/src/ProxyClass/ParamConverter/ViewUIConverter.php
@@ -60,9 +60,7 @@ public function __construct(\Symfony\Component\DependencyInjection\ContainerInte
          */
         protected function lazyLoadItself()
         {
-            if (!isset($this->service)) {
-                $this->service = $this->container->get($this->drupalProxyOriginalServiceId);
-            }
+              $this->service ??= $this->container->get($this->drupalProxyOriginalServiceId);
 
             return $this->service;
         }
diff --git a/core/modules/views_ui/tests/src/FunctionalJavascript/PreviewTest.php b/core/modules/views_ui/tests/src/FunctionalJavascript/PreviewTest.php
index b9afc6146f..32c1533164 100644
--- a/core/modules/views_ui/tests/src/FunctionalJavascript/PreviewTest.php
+++ b/core/modules/views_ui/tests/src/FunctionalJavascript/PreviewTest.php
@@ -306,9 +306,7 @@ protected function assertPreviewAJAX(int $row_count): void {
    * @internal
    */
   protected function assertClass(NodeElement $element, string $class, string $message = ''): void {
-    if (!isset($message)) {
-      $message = "Class .$class found.";
-    }
+    $message ??= "Class .$class found.";
     $this->assertStringContainsString($class, $element->getAttribute('class'), $message);
   }
 
diff --git a/core/modules/workspaces/src/WorkspaceManager.php b/core/modules/workspaces/src/WorkspaceManager.php
index e6663f7ea7..ef34e17659 100644
--- a/core/modules/workspaces/src/WorkspaceManager.php
+++ b/core/modules/workspaces/src/WorkspaceManager.php
@@ -139,11 +139,9 @@ public function __construct(RequestStack $request_stack, EntityTypeManagerInterf
    */
   public function isEntityTypeSupported(EntityTypeInterface $entity_type) {
     $entity_type_id = $entity_type->id();
-    if (!isset($this->supported[$entity_type_id])) {
-      // Only entity types which are revisionable and publishable can belong
-      // to a workspace.
-      $this->supported[$entity_type_id] = $entity_type->entityClassImplements(EntityPublishedInterface::class) && $entity_type->isRevisionable();
-    }
+    // Only entity types which are revisionable and publishable can belong
+    // to a workspace.
+    $this->supported[$entity_type_id] ??= $entity_type->entityClassImplements(EntityPublishedInterface::class) && $entity_type->isRevisionable();
     return $this->supported[$entity_type_id];
   }
 
diff --git a/core/tests/Drupal/KernelTests/AssertContentTrait.php b/core/tests/Drupal/KernelTests/AssertContentTrait.php
index 986a02c92b..2a65e12399 100644
--- a/core/tests/Drupal/KernelTests/AssertContentTrait.php
+++ b/core/tests/Drupal/KernelTests/AssertContentTrait.php
@@ -662,9 +662,7 @@ protected function assertNoPattern($pattern, $message = '') {
    *   TRUE on pass.
    */
   protected function assertTextPattern($pattern, $message = NULL) {
-    if (!isset($message)) {
-      $message = new FormattableMarkup('Pattern "@pattern" found', ['@pattern' => $pattern]);
-    }
+    $message ??= new FormattableMarkup('Pattern "@pattern" found', ['@pattern' => $pattern]);
     $this->assertMatchesRegularExpression($pattern, $this->getTextContent(), $message);
     return TRUE;
   }
diff --git a/core/tests/Drupal/KernelTests/Core/Asset/LibraryDiscoveryIntegrationTest.php b/core/tests/Drupal/KernelTests/Core/Asset/LibraryDiscoveryIntegrationTest.php
index 2466a93259..4b4a6bdf71 100644
--- a/core/tests/Drupal/KernelTests/Core/Asset/LibraryDiscoveryIntegrationTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Asset/LibraryDiscoveryIntegrationTest.php
@@ -302,9 +302,7 @@ protected function activateTheme($theme_name) {
    * @internal
    */
   protected function assertAssetInLibrary(string $asset, string $extension, string $library_name, string $sub_key, string $message = NULL): void {
-    if (!isset($message)) {
-      $message = sprintf('Asset %s found in library "%s/%s"', $asset, $extension, $library_name);
-    }
+    $message ??= sprintf('Asset %s found in library "%s/%s"', $asset, $extension, $library_name);
     $library = $this->libraryDiscovery->getLibraryByName($extension, $library_name);
     foreach ($library[$sub_key] as $definition) {
       if ($asset == $definition['data']) {
@@ -331,9 +329,7 @@ protected function assertAssetInLibrary(string $asset, string $extension, string
    * @internal
    */
   protected function assertNoAssetInLibrary(string $asset, string $extension, string $library_name, string $sub_key, string $message = NULL): void {
-    if (!isset($message)) {
-      $message = sprintf('Asset %s not found in library "%s/%s"', $asset, $extension, $library_name);
-    }
+    $message ??= sprintf('Asset %s not found in library "%s/%s"', $asset, $extension, $library_name);
     $library = $this->libraryDiscovery->getLibraryByName($extension, $library_name);
     foreach ($library[$sub_key] as $definition) {
       if ($asset == $definition['data']) {
diff --git a/core/tests/Drupal/KernelTests/Core/Cache/GenericCacheBackendUnitTestBase.php b/core/tests/Drupal/KernelTests/Core/Cache/GenericCacheBackendUnitTestBase.php
index 0655ba469b..b07e362e78 100644
--- a/core/tests/Drupal/KernelTests/Core/Cache/GenericCacheBackendUnitTestBase.php
+++ b/core/tests/Drupal/KernelTests/Core/Cache/GenericCacheBackendUnitTestBase.php
@@ -49,9 +49,7 @@ abstract class GenericCacheBackendUnitTestBase extends KernelTestBase {
    *   Bin name.
    */
   protected function getTestBin() {
-    if (!isset($this->testBin)) {
-      $this->testBin = 'page';
-    }
+    $this->testBin ??= 'page';
     return $this->testBin;
   }
 
@@ -90,9 +88,7 @@ public function tearDownCacheBackend() {
    *   Cache backend to test.
    */
   protected function getCacheBackend($bin = NULL) {
-    if (!isset($bin)) {
-      $bin = $this->getTestBin();
-    }
+    $bin ??= $this->getTestBin();
     if (!isset($this->cachebackends[$bin])) {
       $this->cachebackends[$bin] = $this->createCacheBackend($bin);
       // Ensure the backend is empty.
diff --git a/core/tests/Drupal/KernelTests/Core/File/FileTestBase.php b/core/tests/Drupal/KernelTests/Core/File/FileTestBase.php
index b41787f452..4601b92e7b 100644
--- a/core/tests/Drupal/KernelTests/Core/File/FileTestBase.php
+++ b/core/tests/Drupal/KernelTests/Core/File/FileTestBase.php
@@ -105,9 +105,7 @@ public function assertFilePermissions($filepath, $expected_mode, $message = NULL
       $expected_mode = $expected_mode | $expected_mode >> 3 | $expected_mode >> 6;
     }
 
-    if (!isset($message)) {
-      $message = t('Expected file permission to be %expected, actually were %actual.', ['%actual' => decoct($actual_mode), '%expected' => decoct($expected_mode)]);
-    }
+    $message ??= t('Expected file permission to be %expected, actually were %actual.', ['%actual' => decoct($actual_mode), '%expected' => decoct($expected_mode)]);
     $this->assertEquals($expected_mode, $actual_mode, $message);
   }
 
@@ -141,9 +139,7 @@ public function assertDirectoryPermissions($directory, $expected_mode, $message
       $expected_mode = $expected_mode | $expected_mode >> 3 | $expected_mode >> 6;
     }
 
-    if (!isset($message)) {
-      $message = t('Expected directory permission to be %expected, actually were %actual.', ['%actual' => decoct($actual_mode), '%expected' => decoct($expected_mode)]);
-    }
+    $message ??= t('Expected directory permission to be %expected, actually were %actual.', ['%actual' => decoct($actual_mode), '%expected' => decoct($expected_mode)]);
     $this->assertEquals($expected_mode, $actual_mode, $message);
   }
 
@@ -159,9 +155,7 @@ public function assertDirectoryPermissions($directory, $expected_mode, $message
    */
   public function createDirectory($path = NULL) {
     // A directory to operate on.
-    if (!isset($path)) {
-      $path = 'public://' . $this->randomMachineName();
-    }
+    $path ??= 'public://' . $this->randomMachineName();
     $this->assertTrue(\Drupal::service('file_system')->mkdir($path));
     $this->assertDirectoryExists($path);
     return $path;
@@ -184,20 +178,16 @@ public function createDirectory($path = NULL) {
    *   File URI.
    */
   public function createUri($filepath = NULL, $contents = NULL, $scheme = NULL) {
-    if (!isset($filepath)) {
-      // Prefix with non-latin characters to ensure that all file-related
-      // tests work with international filenames.
-      // cSpell:disable-next-line
-      $filepath = 'Файл для тестирования ' . $this->randomMachineName();
-    }
+    // Prefix with non-latin characters to ensure that all file-related
+    // tests work with international filenames.
+    // cSpell:disable-next-line
+    $filepath ??= 'Файл для тестирования ' . $this->randomMachineName();
     if (!isset($scheme)) {
       $scheme = 'public';
     }
     $filepath = $scheme . '://' . $filepath;
 
-    if (!isset($contents)) {
-      $contents = "file_put_contents() doesn't seem to appreciate empty strings so let's put in some data.";
-    }
+    $contents ??= "file_put_contents() doesn't seem to appreciate empty strings so let's put in some data.";
 
     file_put_contents($filepath, $contents);
     $this->assertFileExists($filepath);
diff --git a/core/tests/Drupal/KernelTests/KernelTestBase.php b/core/tests/Drupal/KernelTests/KernelTestBase.php
index d89d738e38..c20657b180 100644
--- a/core/tests/Drupal/KernelTests/KernelTestBase.php
+++ b/core/tests/Drupal/KernelTests/KernelTestBase.php
@@ -572,9 +572,7 @@ public function register(ContainerBuilder $container) {
     // Use memory for key value storages to avoid database queries. Store the
     // key value factory on the test object so that key value storages persist
     // container rebuilds, otherwise all state data would vanish.
-    if (!isset($this->keyValue)) {
-      $this->keyValue = new KeyValueMemoryFactory();
-    }
+    $this->keyValue ??= new KeyValueMemoryFactory();
     $container->set('keyvalue', $this->keyValue);
 
     // Set the default language on the minimal container.
diff --git a/core/tests/Drupal/TestTools/Random.php b/core/tests/Drupal/TestTools/Random.php
index e68bc09bb4..9ab875931c 100644
--- a/core/tests/Drupal/TestTools/Random.php
+++ b/core/tests/Drupal/TestTools/Random.php
@@ -23,9 +23,7 @@ abstract class Random {
    *   The random generator.
    */
   public static function getGenerator(): RandomUtility {
-    if (!isset(static::$randomGenerator)) {
-      static::$randomGenerator = new RandomUtility();
-    }
+    static::$randomGenerator ??= new RandomUtility();
     return static::$randomGenerator;
   }
 
diff --git a/core/tests/Drupal/Tests/Component/ProxyBuilder/ProxyBuilderTest.php b/core/tests/Drupal/Tests/Component/ProxyBuilder/ProxyBuilderTest.php
index 1105b3f193..a9ce34e3bb 100644
--- a/core/tests/Drupal/Tests/Component/ProxyBuilder/ProxyBuilderTest.php
+++ b/core/tests/Drupal/Tests/Component/ProxyBuilder/ProxyBuilderTest.php
@@ -379,9 +379,7 @@ public function __construct(\Symfony\Component\DependencyInjection\ContainerInte
          */
         protected function lazyLoadItself()
         {
-            if (!isset($this->service)) {
-                $this->service = $this->container->get($this->drupalProxyOriginalServiceId);
-            }
+              $this->service ??= $this->container->get($this->drupalProxyOriginalServiceId);
 
             return $this->service;
         }
diff --git a/core/tests/Drupal/Tests/Core/Access/AccessManagerTest.php b/core/tests/Drupal/Tests/Core/Access/AccessManagerTest.php
index 74de788258..0c87caca71 100644
--- a/core/tests/Drupal/Tests/Core/Access/AccessManagerTest.php
+++ b/core/tests/Drupal/Tests/Core/Access/AccessManagerTest.php
@@ -531,9 +531,7 @@ protected function setupAccessChecker() {
    * Add default expectations to the access arguments resolver factory.
    */
   protected function setupAccessArgumentsResolverFactory($constraint = NULL) {
-    if (!isset($constraint)) {
-      $constraint = $this->any();
-    }
+    $constraint ??= $this->any();
     return $this->argumentsResolverFactory->expects($constraint)
       ->method('getArgumentsResolver')
       ->willReturnCallback(function ($route_match, $account) {
diff --git a/core/tests/Drupal/Tests/Core/Entity/KeyValueStore/KeyValueEntityStorageTest.php b/core/tests/Drupal/Tests/Core/Entity/KeyValueStore/KeyValueEntityStorageTest.php
index 613bbddb43..93d8e25385 100644
--- a/core/tests/Drupal/Tests/Core/Entity/KeyValueStore/KeyValueEntityStorageTest.php
+++ b/core/tests/Drupal/Tests/Core/Entity/KeyValueStore/KeyValueEntityStorageTest.php
@@ -638,12 +638,8 @@ public function testDeleteNothing() {
   public function getMockEntity($class = EntityBaseTest::class, array $arguments = [], $methods = []) {
     // Ensure the entity is passed at least an array of values and an entity
     // type ID
-    if (!isset($arguments[0])) {
-      $arguments[0] = [];
-    }
-    if (!isset($arguments[1])) {
-      $arguments[1] = 'test_entity_type';
-    }
+    $arguments[0] ??= [];
+    $arguments[1] ??= 'test_entity_type';
     return $this->getMockForAbstractClass($class, $arguments, '', TRUE, TRUE, TRUE, $methods);
   }
 
diff --git a/core/tests/Drupal/Tests/Core/EventSubscriber/ActiveLinkResponseFilterTest.php b/core/tests/Drupal/Tests/Core/EventSubscriber/ActiveLinkResponseFilterTest.php
index 5657fa656a..997b5cb972 100644
--- a/core/tests/Drupal/Tests/Core/EventSubscriber/ActiveLinkResponseFilterTest.php
+++ b/core/tests/Drupal/Tests/Core/EventSubscriber/ActiveLinkResponseFilterTest.php
@@ -292,9 +292,7 @@ public function providerTestSetLinkActiveClass() {
             }
             else {
               $active_attributes = $situation['attributes'];
-              if (!isset($active_attributes['class'])) {
-                $active_attributes['class'] = [];
-              }
+              $active_attributes['class'] ??= [];
               $active_attributes['class'][] = 'is-active';
               $target_markup = $create_markup(new Attribute($active_attributes));
             }
diff --git a/core/tests/Drupal/Tests/Core/Form/FormTestBase.php b/core/tests/Drupal/Tests/Core/Form/FormTestBase.php
index 9de2c5e1ac..b161d36eb2 100644
--- a/core/tests/Drupal/Tests/Core/Form/FormTestBase.php
+++ b/core/tests/Drupal/Tests/Core/Form/FormTestBase.php
@@ -314,9 +314,7 @@ public function getInfo($type) {
       '#name' => 'op',
       '#is_button' => TRUE,
     ];
-    if (!isset($types[$type])) {
-      $types[$type] = [];
-    }
+    $types[$type] ??= [];
     return $types[$type];
   }
 
diff --git a/core/tests/Drupal/Tests/Core/ProxyBuilder/ProxyBuilderTest.php b/core/tests/Drupal/Tests/Core/ProxyBuilder/ProxyBuilderTest.php
index 969c70a345..49f1482db1 100644
--- a/core/tests/Drupal/Tests/Core/ProxyBuilder/ProxyBuilderTest.php
+++ b/core/tests/Drupal/Tests/Core/ProxyBuilder/ProxyBuilderTest.php
@@ -130,9 +130,7 @@ public function __construct(\Symfony\Component\DependencyInjection\ContainerInte
          */
         protected function lazyLoadItself()
         {
-            if (!isset($this->service)) {
-                $this->service = $this->container->get($this->drupalProxyOriginalServiceId);
-            }
+              $this->service ??= $this->container->get($this->drupalProxyOriginalServiceId);
 
             return $this->service;
         }
diff --git a/core/tests/Drupal/Tests/Core/Session/AccessPolicyProcessorTest.php b/core/tests/Drupal/Tests/Core/Session/AccessPolicyProcessorTest.php
index 1eb14c8dab..d7df3b6d39 100644
--- a/core/tests/Drupal/Tests/Core/Session/AccessPolicyProcessorTest.php
+++ b/core/tests/Drupal/Tests/Core/Session/AccessPolicyProcessorTest.php
@@ -402,13 +402,9 @@ protected function setUpAccessPolicyProcessor(
       $cache_static = $cache_static->reveal();
     }
 
-    if (!isset($current_user)) {
-      $current_user = $this->prophesize(AccountProxyInterface::class)->reveal();
-    }
+    $current_user ??= $this->prophesize(AccountProxyInterface::class)->reveal();
 
-    if (!isset($account_switcher)) {
-      $account_switcher = $this->prophesize(AccountSwitcherInterface::class)->reveal();
-    }
+    $account_switcher ??= $this->prophesize(AccountSwitcherInterface::class)->reveal();
 
     return new AccessPolicyProcessor(
       $variation_cache,