public function __construct($parentID = null)
 {
     parent::__construct(false);
     if (is_numeric($parentID)) {
         $parentID += 0;
     }
     if (is_int($parentID)) {
         $this->parent['id'] = (string) $parentID;
     } else {
         throw new \InvalidArgumentException('Parent Issue ID must be INT');
     }
 }