Merge branch '3.1'

* 3.1:
  [CS] Respect PSR2 4.2
  [Form] fix `empty_data` option in expanded `ChoiceType`
  [Console] removed unneeded private methods
  updated Http-Kernel dependency
  [Security] [Guard] Improve comment with working example
  sync min email validator version
  [TwigBridge] Fix inconsistency in LintCommand help
  explicitly forbid e-mail validator 2.0 or higher
  Fixed SymfonyQuestionHelper multi-choice with defaults
  [DoctrineBridge] Don't use object IDs in DoctrineChoiceLoader when passing a value closure
  Differentiate between the first time a progress bar is displayed and subsequent times
  finished previous commit
  No more exception for malformed input name
  fix post_max_size_message translation
  [Process] Fix pipes cleaning on Windows
  Avoid phpunit 5.4 warnings on getMock
  [Form] Add exception to FormRenderer about non-unique block names
  [FrameworkBundle] templating can be fully disabled
  [Form] Consider a violation even if the form is not submitted

Author: fabpot

Guard/GuardAuthenticatorInterface.php

@@ -39,11 +39,15 @@ interface GuardAuthenticatorInterface extends AuthenticationEntryPointInterface
      * Whatever value you return here will be passed to getUser() and checkCredentials()
      *
      * For example, for a form login, you might:
-     *
-     *      return array(
-     *          'username' => $request->request->get('_username'),
-     *          'password' => $request->request->get('_password'),
-     *      );
+     * 
+     *      if ($request->request->has('_username')) {
+     *          return array(
+     *              'username' => $request->request->get('_username'),
+     *              'password' => $request->request->get('_password'),
+     *          );
+     *      } else {
+     *          return;
+     *      }
      *
      * Or for an API token that's on a header, you might use:
      *