Merge branch '4.4' into 5.0

* 4.4:
  Add missing use statements
  [Translation] Add missing use statement
  [Translation] Add missing use statement
  [Config][XmlReferenceDumper] Prevent potential \TypeError
  [Mailer] Fix broken mandrill http send for recipients with names
  [Translation] prefer intl domain when adding messages to catalogue
  Fix CS
  Fix CS
  Fail on empty password verification (without warning on any implementation)
  [Translation][Debug] Add installation and minimal example to README
  [Validator] try to call __get method if property is uninitialized
  Show both missing packages in the same error message
  Fix handling of empty_data's \Closure value in Date/Time form types

Author: fabpot

Definition/Dumper/XmlReferenceDumper.php

@@ -91,7 +91,7 @@ private function writeNode(NodeInterface $node, int $depth = 0, bool $root = fal
                 }
 
                 if ($prototype instanceof PrototypedArrayNode) {
-                    $prototype->setName($key);
+                    $prototype->setName($key ?? '');
                     $children = [$key => $prototype];
                 } elseif ($prototype instanceof ArrayNode) {
                     $children = $prototype->getChildren();