public function getAvatarUrl($email, $size = 80, $extension = 'jpg', $default = 404, $rating = 'g')
    {
        $url = 'https://www.gravatar.com/avatar/';

        $url .= md5(strtolower(trim($email))).'.'.$extension;

        $url .= '?'.http_build_query([
            'd' => $default,
            'r' => $rating,
            's' => $size,
        ]);

        return $url;
    }