public static function extractParamValues($params, &$values) {
        foreach ($params as $k => $v) {
            if (is_array($v) || is_object($v)) {
                self::extractParamValues($v, $values);
            } else {
                if (is_bool($v))  {
                    //if a value is set as false, invalid hash will generate
                    //https://github.com/sailthru/sailthru-php5-client/issues/4
                    $v = intval($v);
                }
                $values[] = $v;
            }
        }
    }