code: public String parseErrorCode(HttpResponse response, JsonContent jsonContent) {
          String errorCodeFromHeader = parseErrorCodeFromHeader(response.getHeaders());
          if (errorCodeFromHeader != null) {
              return errorCodeFromHeader;
          } else if (jsonContent != null) {
              return parseErrorCodeFromContents(jsonContent.getJsonNode());
          } else {
              return null;
          }
      }
docs: Parse the error code from the response.
  
  @return Error Code of exceptional response or null if it can't be determined