[BUGFIX] set default value, to avoid error

Classes/Controller/AbstractBeController.php

@@ -116,7 +116,7 @@ abstract class AbstractBeController extends ActionController
      * @param int $requiredUserGroup UID of the user group
      * @return bool
      */
-    protected function backendUserHasUserGroup($requiredUserGroup)
+    protected function backendUserHasUserGroup($requiredUserGroup=0)
     {
         if (Configuration::AUTH_NONE === $requiredUserGroup) {
             return true;