Merge branch '4.4'

* 4.4:
  cs fix
  Fix return statements
  [TwigBridge] add missing dep
  Add type declarations to private DefaultChoiceListFactory methods
  Add false type to ChoiceListFactoryInterface::createView $label argument
  Update UPGRADE guide of 4.3 for EventDispatcher
  [SecurityBundle] display the correct class name on the deprecated notice

RequestStack.php

@@ -47,7 +47,7 @@ public function push(Request $request)
     public function pop()
     {
         if (!$this->requests) {
-            return;
+            return null;
         }
 
         return array_pop($this->requests);
@@ -73,7 +73,7 @@ public function getCurrentRequest()
     public function getMasterRequest()
     {
         if (!$this->requests) {
-            return;
+            return null;
         }
 
         return $this->requests[0];
@@ -95,7 +95,7 @@ public function getParentRequest()
         $pos = \count($this->requests) - 2;
 
         if (!isset($this->requests[$pos])) {
-            return;
+            return null;
         }
 
         return $this->requests[$pos];