- Constant nulltimerange
constant Calendar.nulltimerange = TimeRange
This represents the null time range, which, to differ from the zero time range (the zero-length time range), isn't placed in time. This is the result of for instance `& between two strict non-overlapping timeranges - no time at all.
It has a constant, is_nulltimerange, which is non-zero. `! on this timerange is true.