public function getUserAttribute()
    {
        if($this->createdByUserID) {

            // search in cache
            $user = User::where('userID', $this->createdByUserID)->first();

            // search in database
            if (!$user) {
                $user = $this->getRelationValue('user');
            }
            return $user;
        }
        return null;
    }