private static void SetFirstRegularPeriodStartDate(InterestRateStream stream,
                                                    DateTime firstRegularPeriodStartDate)
 {
     if (firstRegularPeriodStartDate != new DateTime())
     {
         XsdClassesFieldResolver.CalculationPeriodDatesSetFirstRegularPeriodStartDate(
             stream.calculationPeriodDates, firstRegularPeriodStartDate);
     }
 }