'If blacklisted return an empty response, else return None, which means
that this handler was unable to handle the request and the next one
needs to be called. With this we want to indicate that the keepalive
handler will be called.'

def default_open(self, req):

    if self._is_blacklisted(req.url_object):
        nncr = new_no_content_resp(req.url_object)
        addinfo_inst = http_response_to_httplib(nncr)
        return addinfo_inst
    return None
