docs: protected void assertResponseCode(Request request, Response response) {
      int statusCode = response.code();
      String customMessage = config.getErrorMessages().get(statusCode);
  
      if (response.isSuccessful()) {
        return;
      } else if (customMessage != null) {
        throw requestFailure(request, createStatus(statusCode, combineMessages(customMessage, createStatus(response))));
      } else {
        throw requestFailure(request, createStatus(response));
      }
    }