Merge branch '2.7' into 2.8

* 2.7:
  [HttpKernel] Fix lowest dep
  [Security] fix check for empty usernames
  [Form] updated exception message of ButtonBuilder::setRequestHandler()
  [travis] Fix deps=high jobs
  Fix typo 'assets.package' => 'assets.packages' in UPGRADE-2.7
  [Serializer] Simplify AbstractNormalizer::prepareForDenormalization()
  [HttpFoundation] [PSR-7] Allow to use resources as content body and to return resources from string content
  [DependencyInjection] Remove unused code in XmlFileLoader
  [HttpFoundation] Behaviour change in PHP7 for substr
  bumped Symfony version to 2.3.32
  updated VERSION for 2.3.31
  update CONTRIBUTORS for 2.3.31
  updated CHANGELOG for 2.3.31

Conflicts:
	src/Symfony/Bridge/Twig/composer.json
	src/Symfony/Bundle/FrameworkBundle/composer.json
	src/Symfony/Component/HttpKernel/composer.json

1 files changed, 1 insertions, 1 deletions

diff --git a/Core/User/User.php b/Core/User/User.php
index d458b72..bc81f7f 100644
--- a/Core/User/User.php
+++ b/Core/User/User.php
@@ -30,7 +30,7 @@ final class User implements AdvancedUserInterface
 
     public function __construct($username, $password, array $roles = array(), $enabled = true, $userNonExpired = true, $credentialsNonExpired = true, $userNonLocked = true)
     {
-        if (empty($username)) {
+        if ('' === $username || null === $username) {
             throw new \InvalidArgumentException('The username cannot be empty.');
         }