code: public Optional<UsageData> list(String product, String startDate, String endDate, boolean includeSubaccounts)
      {
          QueryParameterList queryParams = new QueryParameterList();
          if(startDate != null)
              queryParams.add("start_date", startDate);
          if(endDate != null)
              queryParams.add("end_date", endDate);
          queryParams.add("include_subaccounts", includeSubaccounts);
          return HTTP.GET(String.format("/v2/usages/%s.json", product), null, queryParams, USAGE_DATA);
      }
docs: Returns the set of usages with the given parameters.
  @param product The product for the usages
  @param startDate The start date for the usages (YYYY-MM-DD)
  @param endDate The start date for the usages (YYYY-MM-DD)
  @param includeSubaccounts <CODE>true</CODE> if sub-accounts should be included in the usages
  @return The set of usages