Check whether a range is empty

[Alex]

On Tuesday, 17 July 2018 at 13:59:45 UTC, Gary Willoughby wrote:
> I thought every range at the lowest level has an `empty` 
> property. So, in this case, it would be:
>
> if (PFResutl.toRange.empty)
> {
>     writeln("Empty");
> }

Yeah, but it seems, that PFResutl is a range of ranges, and the 
OP has the case, where both of the contained ranges are empty.
However, this does not correspond to empty of the governing range.
So

[[], []].empty is false

whereas

[[], []].joiner.empty is true.