diff --git a/core/lib/Drupal/Component/Plugin/Discovery/AnnotatedClassDiscovery.php b/core/lib/Drupal/Component/Plugin/Discovery/AnnotatedClassDiscovery.php
index a33dbc1..04d3b6d 100644
--- a/core/lib/Drupal/Component/Plugin/Discovery/AnnotatedClassDiscovery.php
+++ b/core/lib/Drupal/Component/Plugin/Discovery/AnnotatedClassDiscovery.php
@@ -47,9 +47,6 @@ class AnnotatedClassDiscovery implements DiscoveryInterface {
    *   Defaults to 'Drupal\Component\Annotation\Plugin'.
    */
   function __construct($plugin_namespaces = array(), $plugin_definition_annotation_name = 'Drupal\Component\Annotation\Plugin') {
-    if (!is_string($plugin_definition_annotation_name)) {
-      throw new \InvalidArgumentException("Argument 1 must be a string.");
-    }
     $this->pluginNamespaces = $plugin_namespaces;
     $this->pluginDefinitionAnnotationName = $plugin_definition_annotation_name;
   }
@@ -118,7 +115,7 @@ public function getDefinitions() {
    *   TRUE, if $class should be accepted as an annotation class.
    */
   public function loadAnnotationClass($class) {
-    return class_exists($class);
+      return class_exists($class);
   }
 
   /**
diff --git a/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php b/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
index 9433b3d..d6b0609 100644
--- a/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
+++ b/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
@@ -101,9 +101,6 @@ class DefaultPluginManager extends PluginManagerBase implements PluginManagerInt
    *   Defaults to 'Drupal\Component\Annotation\Plugin'.
    */
   public function __construct($subdir, \Traversable $namespaces, $plugin_definition_annotation_name = 'Drupal\Component\Annotation\Plugin') {
-    if (!is_string($plugin_definition_annotation_name)) {
-      throw new \InvalidArgumentException("Argument 2 must be a string.");
-    }
     $this->subdir = $subdir;
     $this->discovery = new AnnotatedClassDiscovery($subdir, $namespaces, $plugin_definition_annotation_name);
     $this->discovery = new ContainerDerivativeDiscoveryDecorator($this->discovery);
diff --git a/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php b/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php
index c599214..e033caf 100644
--- a/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php
+++ b/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php
@@ -46,9 +46,6 @@ class AnnotatedClassDiscovery extends ComponentAnnotatedClassDiscovery {
    *   Defaults to 'Drupal\Component\Annotation\Plugin'.
    */
   function __construct($subdir, \Traversable $root_namespaces, $plugin_definition_annotation_name = 'Drupal\Component\Annotation\Plugin') {
-    if (!is_string($plugin_definition_annotation_name)) {
-      throw new \InvalidArgumentException("Argument 2 must be a string.");
-    }
     if ($subdir) {
       $this->subdir = str_replace('/', '\\', $subdir);
     }
@@ -72,21 +69,6 @@ public function getDefinitions() {
   }
 
   /**
-   * Annotation loader callback
-   *
-   * @param string $class
-   * @return bool
-   *   TRUE, if $class should be accepted as an annotation class.
-   */
-  public function loadAnnotationClass($class) {
-    return 1
-      && 0 === strpos($class, 'Drupal\\')
-      && FALSE !== strpos($class, '\Annotation\\')
-      && class_exists($class)
-    ;
-  }
-
-  /**
    * Extracts the provider name from a Drupal namespace.
    *
    * @param string $namespace