Update ServiceContainer.php

src/DependencyInjection/ServiceContainer.php

@@ -45,7 +45,7 @@ class ServiceContainer extends ContainerBuilder
     /**
      * Load service container.
      */
-    public function load($file)
+    public function load($file = null)
     {
         $loader = new YamlFileLoader($this, new FileLocator(__DIR__.'/../Resources/config'));
         $loader->load('config.yml');