Merge branch '2.6' into 2.7

* 2.6:
  [Security] fix check for empty usernames
  [Form] updated exception message of ButtonBuilder::setRequestHandler()
  [travis] Fix deps=high jobs
  [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

2 files changed, 2 insertions, 2 deletions

diff --git a/Core/Authentication/Provider/UserAuthenticationProvider.php b/Core/Authentication/Provider/UserAuthenticationProvider.php
index ded53e4..2674088 100644
--- a/Core/Authentication/Provider/UserAuthenticationProvider.php
+++ b/Core/Authentication/Provider/UserAuthenticationProvider.php
@@ -62,7 +62,7 @@ abstract class UserAuthenticationProvider implements AuthenticationProviderInter
         }
 
         $username = $token->getUsername();
-        if (empty($username)) {
+        if ('' === $username || null === $username) {
             $username = 'NONE_PROVIDED';
         }
 
diff --git a/Core/Authentication/RememberMe/PersistentToken.php b/Core/Authentication/RememberMe/PersistentToken.php
index 92fcb4f..d85572d 100644
--- a/Core/Authentication/RememberMe/PersistentToken.php
+++ b/Core/Authentication/RememberMe/PersistentToken.php
@@ -40,7 +40,7 @@ final class PersistentToken implements PersistentTokenInterface
         if (empty($class)) {
             throw new \InvalidArgumentException('$class must not be empty.');
         }
-        if (empty($username)) {
+        if ('' === $username || null === $username) {
             throw new \InvalidArgumentException('$username must not be empty.');
         }
         if (empty($series)) {