protected function newImportedEventResponse(PhabricatorCalendarEvent $event)
 {
     if (!$event->isImportedEvent()) {
         return null;
     }
     // Give the user a specific, detailed message if they try to edit an
     // imported event via common web paths. Other edits (including those via
     // the API) are blocked by the normal policy system, but this makes it more
     // clear exactly why the event can't be edited.
     return $this->newDialog()->setTitle(pht('Can Not Edit Imported Event'))->appendParagraph(pht('This event has been imported from an external source and ' . 'can not be edited.'))->addCancelButton($event->getURI(), pht('Done'));
 }