public function addEntitySubject($id, $type = null, $idKey = "id", $typeKey = "type")
    {
        if(!isset($this->_subscription->subject)){
            $this->_subscription->subject = (object) [
                "entities" => [],
                "condition" => (object)["attrs" => []]
            ];
        }

        $entity = (object) [];
        $entity->$idKey = $id;

        if (null != $type) {
            $entity->$typeKey = (string)$type;
        }

        $this->_subscription->subject->entities[] = $entity;
        return $this;
    }