Merge branch '3.4' into 4.3

* 3.4:
  Fix inconsistent return points.
  [Security/Core] UserInterface::getPassword() can return null
  [Router] Fix TraceableUrlMatcher behaviour with trailing slash

Author: nicolas-grekas

Firewall/ExceptionListener.php

@@ -92,11 +92,21 @@ public function onKernelException(GetResponseForExceptionEvent $event)
         $exception = $event->getException();
         do {
             if ($exception instanceof AuthenticationException) {
-                return $this->handleAuthenticationException($event, $exception);
-            } elseif ($exception instanceof AccessDeniedException) {
-                return $this->handleAccessDeniedException($event, $exception);
-            } elseif ($exception instanceof LogoutException) {
-                return $this->handleLogoutException($exception);
+                $this->handleAuthenticationException($event, $exception);
+
+                return;
+            }
+
+            if ($exception instanceof AccessDeniedException) {
+                $this->handleAccessDeniedException($event, $exception);
+
+                return;
+            }
+
+            if ($exception instanceof LogoutException) {
+                $this->handleLogoutException($exception);
+
+                return;
             }
         } while (null !== $exception = $exception->getPrevious());
     }

Firewall/UsernamePasswordJsonAuthenticationListener.php

@@ -140,6 +140,9 @@ public function __invoke(RequestEvent $event)
         $event->setResponse($response);
     }
 
+    /**
+     * @return Response|null
+     */
     private function onSuccess(Request $request, TokenInterface $token)
     {
         if (null !== $this->logger) {
@@ -156,7 +159,7 @@ private function onSuccess(Request $request, TokenInterface $token)
         }
 
         if (!$this->successHandler) {
-            return; // let the original request succeeds
+            return null; // let the original request succeeds
         }
 
         $response = $this->successHandler->onAuthenticationSuccess($request, $token);