protected function encode($string)
    {
        if (is_array($string)) {
            foreach ($string as $i => $value) {
                $string[$i] = $this->encode($value);
            }

            return $string;
        }

        if (is_scalar($string)) {
            return str_replace('%7E', '~', rawurlencode($string));
        }

        return null;
    }