code: def _fetch_response_id(self, response):
          
  
          headers = response.headers
  
          if self.HEADER_RESPONSE_ID_UPPER_CASED in headers:
              return headers[self.HEADER_RESPONSE_ID_UPPER_CASED]
  
          if self.HEADER_RESPONSE_ID_LOWER_CASED in headers:
              return headers[self.HEADER_RESPONSE_ID_LOWER_CASED]
  
          return self._ERROR_COULD_NOT_DETERMINE_RESPONSE_ID_HEADER;
docs: :type response: requests.Response
  
          :rtype: str