GET /config
        Get the current compatibility level for a subject.  Result will be one of:

        :param str subject: subject name
        :raises ClientError: if the request was unsuccessful or an invalid compatibility level was returned
        :returns: one of 'NONE','FULL','FORWARD', or 'BACKWARD'
        :rtype: bool

def get_compatibility(self, subject=None):
        """
        GET /config
        Get the current compatibility level for a subject.  Result will be one of:

        :param str subject: subject name
        :raises ClientError: if the request was unsuccessful or an invalid compatibility level was returned
        :returns: one of 'NONE','FULL','FORWARD', or 'BACKWARD'
        :rtype: bool
        """
        url = '/'.join([self.url, 'config'])
        if subject:
            url = '/'.join([url, subject])

        result, code = self._send_request(url)
        is_successful_request = code >= 200 and code <= 299
        if not is_successful_request:
            raise ClientError('Unable to fetch compatibility level. Error code: %d' % code)

        compatibility = result.get('compatibilityLevel', None)
        if compatibility not in VALID_LEVELS:
            if compatibility is None:
                error_msg_suffix = 'No compatibility was returned'
            else:
                error_msg_suffix = str(compatibility)
            raise ClientError('Invalid compatibility level received: %s' % error_msg_suffix)

        return compatibility