Clean existing query string (GET parameters) by removing
        arguments that we don't want to preserve (sort parameter, 'page')

def get_querystring(self):
        """
        Clean existing query string (GET parameters) by removing
        arguments that we don't want to preserve (sort parameter, 'page')
        """
        to_remove = self.get_querystring_parameter_to_remove()
        query_string = urlparse(self.request.get_full_path()).query
        query_dict = parse_qs(query_string.encode('utf-8'))
        for arg in to_remove:
            if arg in query_dict:
                del query_dict[arg]
        clean_query_string = urlencode(query_dict, doseq=True)
        return clean_query_string