public function buildGravatarUrl()
    {
        $base_url = self::HTTPS_GRAVATAR_URL;
        if (!$this->secure) {
            $base_url = self::HTTP_GRAVATAR_URL;
        }
        return $base_url . 'avatar/' . $this->generateAddressHash() . '?s=' . $this->size . '&r=' . $this->rating . '&d=' . $this->default_avatar;
    }