Merge branch '3.3' into 3.4

* 3.3:
  [Dotenv] Get env using $_SERVER to work with fastcgi_param and workaround thread safety issues
  [Dotenv][WebServerBundle] Override previously loaded variables
  [DI] Use GlobResource for non-tracked directories
  [WebProfilerBundle] Re add missing link to the controller

Author: nicolas-grekas

DependencyInjection/FrameworkExtension.php

@@ -1441,7 +1441,7 @@ private function registerSerializerConfiguration(array $config, ContainerBuilder
                 $fileRecorder('yml', $file);
             }
 
-            if ($container->fileExists($dir = $dirname.'/Resources/config/serialization')) {
+            if ($container->fileExists($dir = $dirname.'/Resources/config/serialization', '/^$/')) {
                 $this->registerMappingFilesFromDir($dir, $fileRecorder);
             }
         }