diff --git a/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php b/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
index 2a7e42d..bf6e6ec 100644
--- a/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
+++ b/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
@@ -100,7 +100,7 @@ class DefaultPluginManager extends PluginManagerBase implements PluginManagerInt
   protected $defaults = array();
 
   /**
-   * Defines a fallback ID in case the plugin could not be created.
+   * Defines a fallback ID in case the plugin instance could not be created.
    *
    * @var string
    */
@@ -316,15 +316,16 @@ public function createInstance($plugin_id, array $configuration = array()) {
   }
 
   /**
-   * Returns the plugin ID to be used.
+   * Returns the fallback plugin ID to be used.
    *
    * @param string $original_plugin_id
    *   The plugin ID of the non-instantiable plugin.
    * @param array $configuration
    *   The original configuration of the plugin.
    *
-   * @return string
-   *   The plugin ID of the fallback instance.
+   * @return string|null
+   *   The plugin ID of the fallback instance or NULL if there is no fallback
+   *   set.
    */
   protected function getFallbackPluginId($original_plugin_id, array $configuration) {
     return $this->fallbackPluginId;