Merge branch '5.1' into 5.2

* 5.1:
  [HttpFoundation] Drop int return type from parseFilesize()
  Added $translator->addLoader()
  bug symfony/symfony#39878 [doctrine-bridge] Add username to UserNameNotFoundException
  [Uid] Clarify the format returned by getTime()
  fix spelling
  Add check for constant in Curl client
  Revert #38614, add assert to avoid regression
  Fix container injection with TypedReference
  Fix problem when SYMFONY_PHPUNIT_VERSION is empty string value
  Update PHP CS Fixer config to v2.18

Provider/GuardAuthenticationProvider.php

@@ -105,7 +105,10 @@ private function authenticateViaGuard(AuthenticatorInterface $guardAuthenticator
         $user = $guardAuthenticator->getUser($token->getCredentials(), $this->userProvider);
 
         if (null === $user) {
-            throw new UsernameNotFoundException(sprintf('Null returned from "%s::getUser()".', get_debug_type($guardAuthenticator)));
+            $e = new UsernameNotFoundException(sprintf('Null returned from "%s::getUser()".', get_debug_type($guardAuthenticator)));
+            $e->setUsername($token->getUsername());
+
+            throw $e;
         }
 
         if (!$user instanceof UserInterface) {