Invalid index 'url' on dynamic screens

If a user views a dynamic screen and has "not selected" for the host drop down, the following error is shown at the bottom of the screen:

Undefined index: url [screens.php:176 ? CView->render() ? include() ? CScreenBuilder->show() ? CScreenLldGraphBase->get() ? CScreenBuilder->show() ? CScreenGraph->get() in /var/www/html/web.site.com/include/classes/screens/CScreenGraph.php:149]