docs: public UserStatListResult getUserStatistic(String startTime, int duration)
              throws APIConnectionException, APIRequestException {
          Preconditions.checkArgument(verifyDateFormat("DAY", startTime), "Illegal date format");
          Preconditions.checkArgument(0 <= duration && duration <= 60, " 0 <= duration <= 60");
          String url = mBaseReportPath + mV2StatisticPath + "/users?time_unit=DAY&start=" + startTime + "&duration=" + duration;
          ResponseWrapper responseWrapper = _httpClient.sendGet(url);
          return UserStatListResult.fromResponse(responseWrapper);
      }