fix docblock

src/Silex/Application.php

@@ -470,7 +470,7 @@ class Application extends \Pimple implements HttpKernelInterface, TerminableInte
     /**
      * Handles the request and delivers the response.
      *
-     * @param Request $request Request to process
+     * @param Request|null $request Request to process
      */
     public function run(Request $request = null)
     {