docs: def _CheckGitkitError(self, raw_response):
      """Raises error if API invocation failed.
  
      Args:
        raw_response: string, the http response.
  
      Raises:
        GitkitClientError: if the error code is 4xx.
        GitkitServerError: if the response if malformed.
  
      Returns:
        Successful response as dict.
      """
      try:
        response = simplejson.loads(raw_response)
        if 'error' not in response:
          return response
        else:
          error = response['error']
          if 'code' in error:
            code = error['code']
            if str(code).startswith('4'):
              raise errors.GitkitClientError(error['message'])
            else:
              raise errors.GitkitServerError(error['message'])
      except simplejson.JSONDecodeError:
        pass
      raise errors.GitkitServerError('null error code from Gitkit server')