private static void SetFirstPeriodStartDate(InterestRateStream stream,
                                             AdjustableDate firstPeriodStartDate)
 {
     if (firstPeriodStartDate != null)
     {
         XsdClassesFieldResolver.CalculationPeriodDatesSetFirstPeriodStartDate(
             stream.calculationPeriodDates, firstPeriodStartDate);
     }
 }