@RandyHayes - thanks for clarifying. Yes, this was my misunderstanding. I misread the formula bit as "this is formula that doesn't work", as opposed to "this is the formula I must use to workaround the problem".
@ericonline - I do understand the complexity of this and how frustrating it can be. A similar/related issue is if you want to allow users to update boolean fields in a record, but you don't want to inadvertently update NULL values with false during a Patch.
And if someone can suggest how I can stop hearing Cyndi Lauper in my head whenever I read these threads, that would be appreciated 😉