'is not equal to' not matching NULL isn't a bug. 'is not empty' should not be matching on '---' for select fields.
Dev Note: extensions/RuleEngine/lib/Job.pm sub _custom_search_match_real "$op eq 'isnotempty'" is checking for '---' but perhaps the conditions for that check are flawed?
Hi Laurie, AFAICT 'is empty' and 'is not empty' are working properly, do you have a current example where it fails?