code: public Optional<UsageData> list(String product, long startDate, long endDate, boolean includeSubaccounts)
      {
          return list(product, 
              startDate > 0L ? Utils.getFormattedDate(startDate) : null, 
              endDate > 0L ? Utils.getFormattedDate(endDate) : null, 
              includeSubaccounts);
      }
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 (in milliseconds)
  @param endDate The start date for the usages (in milliseconds)
  @param includeSubaccounts <CODE>true</CODE> if sub-accounts should be included in the usages
  @return The set of usages