Filters: option to select only not valid value?

[paulgirard]

In filters we can ask to show values which are not valid (no value or not valid value).
But we can't see only those N/A cases as filters does not allow to select nothing.
filters only select something or everything but can hardly select nothing at all.
Thus it's not possible to only show the N/A values.
Well actually in a range filter one might be able to do that by selecting an empty range and checking "keep missing values". But that is not possible in a Terms filter.

Should we work on this to allow this usecase?
One motivation would be to curate data during the analysis to isolate the data which have incomplete/incoherent values.

It's not going to be easy to add this feature in all filters.