[Form] Do not set the value attribute for file inputs

src/Symfony/Component/Form/Extension/Core/Type/FileType.php

@@ -51,6 +51,7 @@ class FileType extends AbstractType
     {
         $view->set('multipart', true);
         $view['file']->set('type', 'file');
+        $view['file']->set('value', null);
     }
 
     public function getDefaultOptions(array $options)