[FrameworkBundle] fixed method signature

src/Symfony/Bundle/FrameworkBundle/Controller/ExceptionController.php

@@ -33,7 +33,7 @@ class ExceptionController extends Controller
      *
      * @throws \InvalidArgumentException When the exception template does not exist
      */
-    public function exceptionAction(FlattenException $exception, DebugLoggerInterface $logger, $format, $embedded = false)
+    public function exceptionAction(FlattenException $exception, DebugLoggerInterface $logger = null, $format = 'html', $embedded = false)
     {
         $this['request']->setRequestFormat($format);