[HttpFoundation] Revert getClientIp @return docblock

src/Symfony/Component/HttpFoundation/Request.php

@@ -912,7 +912,7 @@ public function getClientIps()
      * ("Client-Ip" for instance), configure it via the $trustedHeaderSet
      * argument of the Request::setTrustedProxies() method instead.
      *
-     * @return string|null The client IP address
+     * @return string The client IP address
      *
      * @see getClientIps()
      * @see http://en.wikipedia.org/wiki/X-Forwarded-For