[Filter Box] Boolean values show up blank in selector

[vylc]

Make sure these boxes are checked before submitting your issue - thank you!

• I have checked the superset logs for python stacktraces and included it here as text if any
• I have reproduced the issue with at least the latest released version of superset
• I have checked the issue tracker for the same issue and I haven't found one similar

Superset version

Expected results

Should show true/false

Actual results

Shows blank

Steps to reproduce

Add boolean type column to filter section

[mistercrunch]

Presto? Redshift?

[circld]

Also experiencing this behavior on v0.22.1 Postgres tables for any BOOLEAN columns used in a Filter Box slice.

[jakromm]

I'm sure the root cause on this is different, but since you are addressing this code area it might be an easy fix. When exploring a slice and "Enable Filter Select" is enabled, the NULL case in the drop down also shows up as Empty like is shown above. There also doesn't seem to be a way to filter for IS NULL, if you try to use the 'in' predicate it creates an empty set and simply does 1 != 1 (or however you have empty_in_strategy configured for the connection).

[mistercrunch]

related as prerequisite: #4651