private function apiUrl($url = '', $format = 'json')
    {
        if (!$url) {
            return false;
        }

        $absUrl = sprintf('https://%s/pms/v%d/%s/%s', 
                          $this->apiBase,
                          $this->version,
                          $format,
                          $url);

        return (string) $absUrl;
    }