public function setLastPost($lastPost)
    {
        if ($lastPost == 0) {
            $this->_lastPost = "";
        } elseif ($lastPost !== "" and $lastPost !== "NULL" and $lastPost !== null) {
            if ($lastPost instanceof DateTime) {
                $this->_lastPost = $lastPost;
            } else {
                $this->_lastPost = new DateTime($lastPost);
            }
        }
        return $this;
    }