Merge branch '4.2'

* 4.2: (27 commits)
  cs fix
  cs fix
  [PHPUnit-Bridge] override some environment variables
  [TwigBridge] Remove use spaceless tag
  Upgrade zookeeper ext
  [translation] Update defaut format from yml to yaml
  Change default log level for output streams
  update docblock to match the actual behavior
  Don't resolve the Deprecation error handler mode until a deprecation is triggered
  compatibility with phpunit8
  Make 'headers' key optional for encoded messages
  [Debug][DebugClassLoader] Detect annotations before blank docblock lines on final and internal methods
  Fix undefined variable fromConstructor when passing context to getTypes
  Added translations for chineese language.
  Allow 3rd argument to be null
  Remove whitespace (tab on blank line)
  [Monolog] Really reset logger when calling logger::reset()
  [Form] Fixes debug:form appears many times as type extensions configured with new getExtendedTypes method
  Update src/Symfony/Component/PropertyInfo/Tests/Extractor/ReflectionExtractorTest.php
  Update src/Symfony/Component/PropertyInfo/Tests/Extractor/ReflectionExtractorTest.php
  ...

Author: nicolas-grekas

Container.php

@@ -138,7 +138,7 @@ public function setParameter($name, $value)
     /**
      * Sets a service.
      *
-     * Setting a service to null resets the service: has() returns false and get()
+     * Setting a synthetic service to null resets it: has() returns false and get()
      * behaves in the same way as if the service was never created.
      *
      * @param string $id      The service identifier