diff --git a/core/lib/Drupal/Component/Plugin/DefaultPluginBag.php b/core/lib/Drupal/Component/Plugin/DefaultPluginBag.php
index 8e64a88..ccffb4e 100644
--- a/core/lib/Drupal/Component/Plugin/DefaultPluginBag.php
+++ b/core/lib/Drupal/Component/Plugin/DefaultPluginBag.php
@@ -7,9 +7,8 @@
 
 namespace Drupal\Component\Plugin;
 
-use Drupal\Component\Plugin\Exception\PluginException;
+use Drupal\Component\Plugin\Exception\UnknownPluginException;
 use Drupal\Component\Utility\MapArray;
-use Drupal\Component\Utility\String;
 
 /**
  * Provides a default plugin bag for a plugin type.
@@ -66,11 +65,11 @@ public function __construct(PluginManagerInterface $manager, array $configuratio
    */
   protected function initializePlugin($instance_id) {
     if (!isset($this->configurations[$instance_id])) {
-      throw new PluginException(String::format("Unknown plugin ID '@instance'.", array('@instance' => $instance_id)));
+      throw new UnknownPluginException($instance_id);
     }
     $configuration = $this->configurations[$instance_id];
     if (!isset($configuration[$this->pluginKey])) {
-      throw new PluginException(String::format("Unknown plugin ID '@instance'.", array('@instance' => $instance_id)));
+      throw new UnknownPluginException($instance_id);
     }
     $this->pluginInstances[$instance_id] = $this->manager->createInstance($configuration[$this->pluginKey], $configuration);
     $this->addInstanceID($instance_id);
diff --git a/core/lib/Drupal/Component/Plugin/Exception/UnknownPluginException.php b/core/lib/Drupal/Component/Plugin/Exception/UnknownPluginException.php
new file mode 100644
index 0000000..6c8804f
--- /dev/null
+++ b/core/lib/Drupal/Component/Plugin/Exception/UnknownPluginException.php
@@ -0,0 +1,31 @@
+<?php
+/**
+ * @file
+ * Definition of Drupal\Component\Plugin\Exception\UnknownPluginException.
+ */
+
+namespace Drupal\Component\Plugin\Exception;
+
+use Drupal\Component\Utility\String;
+
+/**
+ * Plugin exception class to be thrown when a nonexistent plugin was requested.
+ */
+class UnknownPluginException extends PluginException {
+
+  /**
+   * Construct an UnknownPluginException exception.
+   *
+   * @param string $instance_id
+   *   The invalid instance ID that failed.
+   *
+   * @see \Exception for remaining parameters.
+   */
+  public function __construct($instance_id, $message = '', $code = 0, \Exception $previous = NULL) {
+    if (empty($message)) {
+      $message = String::format("Unknown plugin ID '@instance'.", array('@instance' => $instance_id));
+    }
+    parent::__construct($message, $code, $previous);
+  }
+
+}
diff --git a/core/lib/Drupal/Component/Plugin/PluginBag.php b/core/lib/Drupal/Component/Plugin/PluginBag.php
index 3f77e03..e37b367 100644
--- a/core/lib/Drupal/Component/Plugin/PluginBag.php
+++ b/core/lib/Drupal/Component/Plugin/PluginBag.php
@@ -7,8 +7,6 @@
 
 namespace Drupal\Component\Plugin;
 
-use Drupal\Component\Plugin\Exception\PluginException;
-
 /**
  * Defines an object which stores multiple plugin instances to lazy load them.
  *
@@ -67,13 +65,7 @@ public function has($instance_id) {
    */
   public function &get($instance_id) {
     if (!isset($this->pluginInstances[$instance_id])) {
-      try {
-        $this->initializePlugin($instance_id);
-      }
-      catch (PluginException $e) {
-        $null = NULL;
-        return $null;
-      }
+      $this->initializePlugin($instance_id);
     }
     return $this->pluginInstances[$instance_id];
   }
diff --git a/core/modules/image/image.module b/core/modules/image/image.module
index 5610303..d22c658 100644
--- a/core/modules/image/image.module
+++ b/core/modules/image/image.module
@@ -6,6 +6,7 @@
  */
 
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Component\Plugin\Exception\UnknownPluginException;
 use Drupal\field\Plugin\Core\Entity\Field;
 use Drupal\field\Plugin\Core\Entity\FieldInstance;
 use Drupal\file\Plugin\Core\Entity\File;
@@ -72,12 +73,14 @@ function image_help($path, $arg) {
       $effect = Drupal::service('plugin.manager.image.effect')->getDefinition($arg[7]);
       return isset($effect['description']) ? ('<p>' . $effect['description'] . '</p>') : NULL;
     case 'admin/config/media/image-styles/manage/%/effects/%':
-      $effect = entity_load('image_style', $arg[5])->getEffect($arg[7]);
-      if (empty($effect)) {
+      try {
+        $effect = entity_load('image_style', $arg[5])->getEffect($arg[7]);
+      }
+      catch (UnknownPluginException $e) {
         return NULL;
       }
-      $definition = $effect->getPluginDefinition();
-      return isset($definition['description']) ? ('<p>' . $definition['description'] . '</p>') : NULL;
+      $effect_definition = $effect->getPluginDefinition();
+      return isset($effect_definition['description']) ? ('<p>' . $effect_definition['description'] . '</p>') : NULL;
   }
 }
 
diff --git a/core/modules/image/lib/Drupal/image/Form/ImageEffectFormBase.php b/core/modules/image/lib/Drupal/image/Form/ImageEffectFormBase.php
index dbfaf49..d171e47 100644
--- a/core/modules/image/lib/Drupal/image/Form/ImageEffectFormBase.php
+++ b/core/modules/image/lib/Drupal/image/Form/ImageEffectFormBase.php
@@ -10,6 +10,7 @@
 use Drupal\Core\Form\FormInterface;
 use Drupal\image\ConfigurableImageEffectInterface;
 use Drupal\image\ImageStyleInterface;
+use Drupal\Component\Plugin\Exception\UnknownPluginException;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
@@ -57,8 +58,10 @@ public function getFormID() {
    */
   public function buildForm(array $form, array &$form_state, Request $request = NULL, ImageStyleInterface $image_style = NULL, $image_effect = NULL) {
     $this->imageStyle = $image_style;
-    $this->imageEffect = $this->prepareImageEffect($image_effect);
-    if (empty($this->imageEffect)) {
+    try {
+      $this->imageEffect = $this->prepareImageEffect($image_effect);
+    }
+    catch (UnknownPluginException $e) {
       throw new NotFoundHttpException();
     }
 
diff --git a/core/modules/image/lib/Drupal/image/Tests/ImageAdminStylesTest.php b/core/modules/image/lib/Drupal/image/Tests/ImageAdminStylesTest.php
index 78a5838..e3aece9 100644
--- a/core/modules/image/lib/Drupal/image/Tests/ImageAdminStylesTest.php
+++ b/core/modules/image/lib/Drupal/image/Tests/ImageAdminStylesTest.php
@@ -347,10 +347,10 @@ function testEditEffect() {
     $this->assertText(t('Scale 24x19'));
     $this->assertText(t('Scale 12x19'));
 
-    // Try to edit an inexisting effect.
+    // Try to edit a nonexistent effect.
     $uuid = new Uuid();
     $this->drupalGet('admin/config/media/image-styles/manage/' . $style_name . '/effects/' . $uuid->generate());
-    $this->assertResponse(401);
+    $this->assertResponse(404);
   }
 
   /**