public Period(IDateTime start, IDateTime end)
{
if (end != null && end.LessThanOrEqual(start))
{
throw new ArgumentException($"Start time ( {start} ) must come before the end time ( {end} )");
}
StartTime = start;
if (end == null)
{
return;
}
EndTime = end;
Duration = end.Subtract(start);
}