public function handle(PageEvent $event)
 {
     $page = $event->getPage();
     $title = $event->getNewTitle();
     if ($title !== Page::DEFAULT_TITLE && empty($page->getInternalName())) {
         $slug = Str::slug($title);
         $unique = Str::unique($slug, function ($name) {
             return PageFacade::internalNameExists($name) === false;
         });
         $page->setInternalName($unique);
         PageFacade::save($page);
     }
 }