diff --git a/core/includes/menu.inc b/core/includes/menu.inc
index 6df8d30..e94f4c8 100644
--- a/core/includes/menu.inc
+++ b/core/includes/menu.inc
@@ -17,6 +17,7 @@
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
 use Symfony\Component\Routing\Route;
+use Drupal\menu_link\MenuLinkInterface;
 
 /**
  * @defgroup menu Menu system
@@ -637,19 +638,14 @@ function _menu_check_access(&$item, $map) {
  */
 function _menu_item_localize(&$item, $map, $link_translate = FALSE) {
   $title_callback = $item['title_callback'];
-  $item['localized_options'] = $item['options'];
+  $options = $item['options'];
   // All 'class' attributes are assumed to be an array during rendering, but
   // links stored in the database may use an old string value.
   // @todo In order to remove this code we need to implement a database update
   //   including unserializing all existing link options and running this code
   //   on them, as well as adding validation to menu_link_save().
-  if (isset($item['options']['attributes']['class']) && is_string($item['options']['attributes']['class'])) {
-    if ($item instanceof MenuLinkInterface) {
-      $item->localized_options->attributes['class'] = explode(' ', $item->options->attributes['class']);
-    }
-    else {
-      $item['localized_options']['attributes']['class'] = explode(' ', $item['options']['attributes']['class']);
-    }
+  if (isset($options['attributes']['class']) && is_string($options['attributes']['class'])) {
+    $options['attributes']['class'] = explode(' ', $options['attributes']['class']);
   }
   // If we are translating the title of a menu link, and its title is the same
   // as the corresponding router item, then we can use the title information
@@ -677,12 +673,7 @@ function _menu_item_localize(&$item, $map, $link_translate = FALSE) {
       }
       // Avoid calling check_plain again on l() function.
       if ($title_callback == 'check_plain') {
-        if ($item instanceof MenuLinkInterface) {
-          $item->localized_options->html = TRUE;
-        }
-        else {
-          $item['localized_options']['html'] = TRUE;
-        }
+        $options['html'] = TRUE;
       }
     }
   }
@@ -718,8 +709,15 @@ function _menu_item_localize(&$item, $map, $link_translate = FALSE) {
   }
   // If the title and description are the same, use the translated description
   // as a localized title.
-  if ($link_translate && isset($original_description) && isset($item['options']['attributes']['title']) && $item->options->attributes['title'] == $original_description) {
-    $item->localized_options->setValue(array('title' => $item['description']) + $item['localized_options']['attributes']);
+  if ($link_translate && isset($original_description) && isset($options['attributes']['title']) && $options['attributes']['title'] == $original_description) {
+    $options['title'] = $item['description'];
+  }
+
+  if ($item instanceof MenuLinkInterface) {
+    $item->localized_options->setValue($options);
+  }
+  else {
+    $item['localized_options'] = $options;
   }
 }
 
diff --git a/core/lib/Drupal/Core/Entity/Plugin/DataType/MapItem.php b/core/lib/Drupal/Core/Entity/Plugin/DataType/MapItem.php
index 065991a..b79aa6d 100644
--- a/core/lib/Drupal/Core/Entity/Plugin/DataType/MapItem.php
+++ b/core/lib/Drupal/Core/Entity/Plugin/DataType/MapItem.php
@@ -24,25 +24,13 @@
 class MapItem extends FieldItemBase {
 
   /**
-   * {@inheritdoc}
-   */
-  public function getPropertyDefinitions() {
-    $definitions = array();
-    foreach ($this->properties as $name => $property) {
-      $definitions[$name] = $property->getDefinition();
-    }
-
-    return $definitions;
-  }
-
-  /**
    * Overrides \Drupal\Core\Entity\Field\FieldItemBase::setValue().
    *
    * @param array|null $values
    *   An array of property values.
    */
   public function setValue($values, $notify = TRUE) {
-    $this->properties = array();
+    $this->values = array();
     if (!isset($values)) {
       return;
     }
@@ -56,40 +44,23 @@ public function setValue($values, $notify = TRUE) {
       }
     }
 
-    foreach($values as $name => $value) {
-      $this->properties[$name] = $this->valueToProperty($value, $name);
-    }
+    $this->values = $values;
   }
 
   public function __get($name) {
-    if (!isset($this->properties[$name])) {
-      $this->properties[$name] = $this->valueToProperty(array(), $name);
+    if (!isset($this->values[$name])) {
+      $this->values[$name] = array();
     }
 
-    return $this->properties[$name]->getValue();
+    return $this->values[$name];
   }
 
   public function __set($name, $value) {
     if (isset($value)) {
-      if (isset($this->properties[$name])) {
-        $this->properties[$name]->setValue($value);
-      }
-      else {
-        $this->properties[$name] = $this->valueToProperty($value, $name);
-      }
+      $this->values[$name] = $value;
     }
     else {
-      unset($this->properties[$name]);
+      unset($this->values[$name]);
     }
   }
-
-  protected function valueToProperty($value, $name) {
-    $def = array('type' => 'any');
-    if ($value instanceof TypedData) {
-      $def = $value->getDefinition();
-      $value = $value->getValue();
-    }
-
-    return \Drupal::typedData()->create($def, $value, $name, $this);
-  }
 }
diff --git a/core/modules/menu_link/lib/Drupal/menu_link/Entity/MenuLink.php b/core/modules/menu_link/lib/Drupal/menu_link/Entity/MenuLink.php
index 4a1e0fe..2e19708 100644
--- a/core/modules/menu_link/lib/Drupal/menu_link/Entity/MenuLink.php
+++ b/core/modules/menu_link/lib/Drupal/menu_link/Entity/MenuLink.php
@@ -153,8 +153,7 @@ public function bundle() {
    */
   public function createDuplicate() {
     $duplicate = parent::createDuplicate();
-
-    $duplicate->get('plid')->offsetGet(0)->set('value', NULL);
+    $duplicate->setParentLinkId(NULL);
     return $duplicate;
   }
 
@@ -621,7 +620,7 @@ public function setRouterPath($router_path) {
    * {@inheritdoc}
    */
   public function getOptions() {
-    return $this->get('options')->value;
+    return $this->get('options')->getValue();
   }
 
   /**
@@ -794,7 +793,7 @@ public function setAccess($access) {
    * {@inheritdoc}
    */
   public function getRouteParams() {
-    return $this->get('route_parameters')->value;
+    return $this->get('route_parameters')->getValue();
   }
 
   /**
diff --git a/core/modules/menu_link/lib/Drupal/menu_link/MenuLinkStorageController.php b/core/modules/menu_link/lib/Drupal/menu_link/MenuLinkStorageController.php
index 08ca34c..44f8cff 100644
--- a/core/modules/menu_link/lib/Drupal/menu_link/MenuLinkStorageController.php
+++ b/core/modules/menu_link/lib/Drupal/menu_link/MenuLinkStorageController.php
@@ -160,8 +160,8 @@ protected function mapFromStorageRecords(array $records, $load_revision = FALSE)
   /**
    * {@inheritdoc}
    */
-  protected function mapToStorageRecord(EntityInterface $entity) {
-    $record = parent::mapToStorageRecord($entity);
+  protected function mapToStorageRecord(EntityInterface $entity, $table_key = 'base_table') {
+    $record = parent::mapToStorageRecord($entity, $table_key);
     foreach (array('options', 'route_parameters') as $property) {
       $record->$property = $entity->$property->getValue();
     }
diff --git a/core/modules/system/lib/Drupal/system/Controller/SystemController.php b/core/modules/system/lib/Drupal/system/Controller/SystemController.php
index d0c36d9..be60855 100644
--- a/core/modules/system/lib/Drupal/system/Controller/SystemController.php
+++ b/core/modules/system/lib/Drupal/system/Controller/SystemController.php
@@ -91,9 +91,11 @@ public function overview() {
           }
           // The link description, either derived from 'description' in hook_menu()
           // or customized via menu module is used as title attribute.
-          if (!empty($item->localized_options->attributes['title'])) {
-            $item['description'] = $item->localized_options->attributes['title'];
-            unset($item->localized_options->attributes['title']);
+          $attrs = $item->localized_options->attributes;
+          if (!empty($attrs['title'])) {
+            $item['description'] = $attrs['title'];
+            unset($attrs['title']);
+            $item->localized_options->attributes = $attrs;
           }
           $block = array(
             'title' => $item->getLinkTitle(),
diff --git a/core/modules/system/lib/Drupal/system/SystemManager.php b/core/modules/system/lib/Drupal/system/SystemManager.php
index f2e8973..82733f4 100644
--- a/core/modules/system/lib/Drupal/system/SystemManager.php
+++ b/core/modules/system/lib/Drupal/system/SystemManager.php
@@ -212,9 +212,11 @@ public function getAdminBlock($item) {
       if ($link->getAccess()) {
         // The link description, either derived from 'description' in
         // hook_menu() or customized via menu module is used as title attribute.
-        if (!empty($link->localized_options->attributes['title'])) {
-          $link['description'] = $link->localized_options->attributes['title'];
-          unset($link->localized_options->attributes['title']);
+        $attrs = $link->localized_options->attributes;
+        if (!empty($attrs['title'])) {
+          $link['description'] = $attrs['title'];
+          unset($attrs['title']);
+          $link->localized_options->attributes = $attrs;
         }
         // Prepare for sorting as in function _menu_tree_check_access().
         // The weight is offset so it is always positive, with a uniform 5-digits.