code: private static boolean _isValidInYear (@Nonnull final Holiday aHoliday, final int nYear)
    {
      return (aHoliday.getValidFrom () == null || aHoliday.getValidFrom ().intValue () <= nYear) &&
             (aHoliday.getValidTo () == null || aHoliday.getValidTo ().intValue () >= nYear);
    }
docs: Checks whether the holiday is within the valid date range.
  
  @param aHoliday
  @param nYear
  @return is valid.