/**
  * Return array of subscribed users
  *
  * @param void
  * @return array
  */
 function getSubscribers()
 {
     if ($this->subscribers === false) {
         $this->subscribers = $this->can_have_subscribers ? Subscriptions::findSubscribersByParent($this) : null;
     }
     // if
     return $this->subscribers;
 }