fix type for condition in ParticipationController

src/Bundle/ChillEventBundle/Controller/ParticipationController.php

@@ -235,7 +235,7 @@ class ParticipationController extends AbstractController
                 'The participation was created'
             ));
 
-            if ($request->query->get('return_path')) {
+            if ($request->query->has('return_path')) {
                 return $this->redirect($request->query->get('return_path'));
             }
 
@@ -716,7 +716,7 @@ class ParticipationController extends AbstractController
      */
     protected function newSingle(Request $request)
     {
-        $returnPath = $request->query->get('return_path') ?
+        $returnPath = $request->query->has('return_path') ?
                 $request->query->get('return_path') : null;
 
         $participation = $this->handleRequest($request, new Participation(), false);