Hot fix

Author: fabpot

DependencyInjection/Configuration.php

@@ -1516,7 +1516,9 @@ private function addNotifierSection(ArrayNodeDefinition $rootNode)
                             ->prototype('scalar')->end()
                         ->end()
                     ->end()
-                    ->booleanNode('notification_on_failed_messages')->defaultFalse()->end()
+                    ->children()
+                        ->booleanNode('notification_on_failed_messages')->defaultFalse()->end()
+                    ->end()
                     ->children()
                         ->arrayNode('channel_policy')
                             ->useAttributeAsKey('name')