Merge branch '3.4' into 4.3

* 3.4: (21 commits)
  [SecurityBundle] fix return type declarations
  [BrowserKit] fix return type declarations
  [PropertyInfo] fix return type declarations
  [Bridge/Doctrine] fix return type declarations
  [Form] fix return type declarations
  [Console] fix return type declarations
  [Intl] fix return type declarations
  [Templating] fix return type declarations
  [DomCrawler] fix return type declarations
  [Validator] fix return type declarations
  [Process] fix return type declarations
  [Workflow] fix return type declarations
  [Cache] fix return type declarations
  [Serializer] fix return type declarations
  [Translation] fix return type declarations
  [DI] fix return type declarations
  [Config] fix return type declarations
  [HttpKernel] Fix return type declarations
  [Security] Fix return type declarations
  [Routing] Fix return type declarations
  ...

Author: nicolas-grekas

Context/ExecutionContextInterface.php

@@ -283,7 +283,7 @@ public function getMetadata();
     /**
      * Returns the validation group that is currently being validated.
      *
-     * @return string The current validation group
+     * @return string|null The current validation group
      */
     public function getGroup();