[HttpKernel] fixed Request::getETags()

src/Symfony/Components/HttpKernel/Request.php

@@ -462,7 +462,7 @@ class Request
 
     public function getETags()
     {
-        return preg_split('/\s*,\s*/', $this->headers->get('if_none_match'));
+        return preg_split('/\s*,\s*/', $this->headers->get('if_none_match'), null, PREG_SPLIT_NO_EMPTY);
     }
 
     public function isNoCache()