private function ensureNodeSubscribers(NodeEvent $event)
    {
        $node = $event->getNode();

        $followers = [];

        if ($userId = $node->getOwnerId()) {
            $followers[] = $userId;
        }
        if ($userId = $this->currentUser->id()) {
            $followers[] = $userId;
        }

        if ($this->siteManager && $node->site_id) {
            // Notify all webmasters for the site, useful for content modified by local contributors.
            $site = $this->siteManager->getStorage()->findOne($node->site_id);
            foreach ($this->siteManager->getAccess()->listWebmasters($site) as $webmaster) {
                $followers[] = $webmaster->getUserId();
            }
        }

        $this->service->getNotificationService()->subscribe('node', $node->id(), $followers);
    }