public WorkingPeriodViewModel(When monthYear)
{
Year = monthYear.Year;
// ReSharper disable once PossibleNullReferenceException
AvailableMonths = DateTimeFormatInfo.CurrentInfo.MonthNames
.Zip(Enumerable.Range(1, 12), (name, index) => new Month(index, name));
Month = AvailableMonths.Single(x => x.Index == monthYear.Month);
}
