Serialize as a URL for a GET request.

def to_url(self):
        """Serialize as a URL for a GET request."""
        base_url = urlparse(self.url)

        query = parse_qs(base_url.query)
        for k, v in self.items():
            query.setdefault(k, []).append(to_utf8_optional_iterator(v))
        scheme = base_url.scheme
        netloc = base_url.netloc
        path = base_url.path
        params = base_url.params
        fragment = base_url.fragment

        url = (scheme, netloc, path, params, urlencode(query, True), fragment)
        return urlunparse(url)