diff --git a/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php b/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php
index 3c10366..e356c3b 100644
--- a/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php
+++ b/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php
@@ -39,8 +39,10 @@ function __construct($owner, $type, array $root_namespaces = array()) {
       'Drupal\Core\Annotation' => DRUPAL_ROOT . '/core/lib',
     );
     $plugin_namespaces = array();
-    foreach ($root_namespaces as $namespace => $dir) {
-      $plugin_namespaces["$namespace\\Plugin\\{$owner}\\{$type}"] = array($dir);
+    if (!empty($root_namespaces)) {
+      foreach ($root_namespaces as $namespace => $dir) {
+        $plugin_namespaces["$namespace\\Plugin\\{$owner}\\{$type}"] = array($dir);
+      }
     }
     parent::__construct($plugin_namespaces, $annotation_namespaces);
   }