Merge branch '3.4' into 4.1

* 3.4:
  [Debug] ignore underscore vs backslash namespaces in DebugClassLoader
  [TwigBridge][Form] Prevent multiple rendering of form collection prototypes
  [FrameworkBundle] fix describing routes with no controllers
  [DI] move RegisterServiceSubscribersPass before DecoratorServicePass
  Update ValidationListener.php
  [Yaml] ensures that the mb_internal_encoding is reset to its initial value
  [WebLink] Fixed documentation link
  [Security] getTargetPath of TargetPathTrait must return string or null
  [Hackday][Serializer] Deserialization ignores argument type hint from phpdoc for array in constructor argument
  [Security] defer log message in guard authenticator
  merge conflicts
  Fix HeaderBag::get phpdoc

Author: nicolas-grekas

Console/Descriptor/TextDescriptor.php

@@ -56,7 +56,7 @@ protected function describeRouteCollection(RouteCollection $routes, array $optio
 
             if ($showControllers) {
                 $controller = $route->getDefault('_controller');
-                $row[] = $this->formatCallable($controller);
+                $row[] = $controller ? $this->formatCallable($controller) : '';
             }
 
             $tableRows[] = $row;