public RegularTimePeriod next() {
        Month result;
        if (this.month != MonthConstants.DECEMBER) {
            result = new Month(this.month + 1, this.year);
        }
        else {
            if (this.year < 9999) {
                result = new Month(MonthConstants.JANUARY, this.year + 1);
            }
            else {
                result = null;
            }
        }
        return result;