public function username($readable = false)
 {
     if ($readable === false) {
         return $this->get('username');
     } else {
         return \OGM\Util\UserUtil::formatUsername($this->get('username'));
     }
 }
 public function __construct($userID)
 {
     $this->userID = $userID;
     //check userID
     if (!\OGM\Util\UserUtil::verify($userID)) {
         throw new \OGM\Exception\SystemException('Invalid user, userID = ' . $userID);
     }
 }