Flarum\Api\Serializer\NotificationSerializer::setSubjectSerializer PHP Method

    public static function setSubjectSerializer($type, $serializer)
    {
        static::$subjectSerializers[$type] = $serializer;
    }

 /**
  * Register notification serializers.
  */
 protected function registerNotificationSerializers()
 {
     $blueprints = [];
     $serializers = ['discussionRenamed' => 'Flarum\\Api\\Serializer\\DiscussionBasicSerializer'];
     $this->app->make('events')->fire(new ConfigureNotificationTypes($blueprints, $serializers));
     foreach ($serializers as $type => $serializer) {
         NotificationSerializer::setSubjectSerializer($type, $serializer);
     }
 }