minor #883 removal of redundant line of code (aambr)

This PR was merged into the 1.2.x-dev branch.

Discussion
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removal of redundant line of code

Commits
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539e97eb removal of redundant line of code

src/Silex/Application.php

@@ -122,8 +122,6 @@ class Application extends \Pimple implements HttpKernelInterface, TerminableInte
             if (class_exists('Symfony\Component\HttpFoundation\RequestStack')) {
                 return new RequestStack();
             }
-
-            return null;
         });
 
         $this['request_context'] = $this->share(function () use ($app) {