diff --git a/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php b/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
index 9b08432..8173c68 100644
--- a/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
+++ b/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
@@ -22,7 +22,7 @@
 /**
  * Base class for plugin managers.
  */
-abstract class DefaultPluginManager extends PluginManagerBase implements PluginManagerInterface, CachedDiscoveryInterface {
+class DefaultPluginManager extends PluginManagerBase implements PluginManagerInterface, CachedDiscoveryInterface {
 
   /**
    * Cached definitions array.
@@ -106,13 +106,13 @@ public function __construct($subdir, \Traversable $namespaces, $annotation_names
    * Initialize the cache backend.
    *
    * Plugin definitions are cached using the provided cache backend. The
-   * interface languge is added as a suffix to the cache key.
+   * interface language is added as a suffix to the cache key.
    *
    * @param \Drupal\Core\Cache\CacheBackendInterface $cache
    *   Cache backend instance to use.
    * @param \Drupal\Core\Language\LanguageManager
    *   The language manager.
-   * @param type $cache_key_prefix
+   * @param string $cache_key_prefix
    *   Cache key prefix to use, the language code will be appended
    *   automatically.
    */
@@ -126,7 +126,7 @@ public function setCache(CacheBackendInterface $cache, LanguageManager $language
   /**
    * Initializes the alter hook.
    *
-   * @param \Drupal\Core\Extension\ModuleHandler $module_handler
+   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
    *   The module handler to invoke the alter hook with.
    * @param string $alter_hook
    *   Name of the alter hook.
@@ -148,6 +148,7 @@ public function getDefinition($plugin_id) {
     if (isset($this->definitions[$plugin_id])) {
       return $this->definitions[$plugin_id];
     }
+    return array();
   }
 
   /**
diff --git a/core/tests/Drupal/Tests/Core/Plugin/TestPluginManager.php b/core/tests/Drupal/Tests/Core/Plugin/TestPluginManager.php
index 746adcf..b7fe091 100644
--- a/core/tests/Drupal/Tests/Core/Plugin/TestPluginManager.php
+++ b/core/tests/Drupal/Tests/Core/Plugin/TestPluginManager.php
@@ -21,13 +21,15 @@ class TestPluginManager extends DefaultPluginManager {
    *
    * @param \Traversable $namespaces
    *   An object that implements \Traversable which contains the root paths
-   *   keyed by the corresponding namespace to look for plugin implementations,
-   * @param \Drupal\Core\Extension\ModuleHandler $module_handler
+   *   keyed by the corresponding namespace to look for plugin implementations.
+   * @param array $definitions
+   *   An array of static definitions.
+   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
    *   (optional) The module handler to invoke the alter hook with.
    * @param string $alter_hook
    *   (optional) Name of the alter hook.
    */
-  public function __construct(\Traversable $namespaces, $definitions, ModuleHandlerInterface $module_handler = NULL, $alter_hook = NULL) {
+  public function __construct(\Traversable $namespaces, array $definitions, ModuleHandlerInterface $module_handler = NULL, $alter_hook = NULL) {
     // Create the object that can be used to return definitions for all the
     // plugins available for this type. Most real plugin managers use a richer
     // discovery implementation, but StaticDiscovery lets us add some simple