It's been a while since relational algebra so I don't feel confident saying "Yes" or "No" (I guess you could say my reply is Null) - but that seems like a really good base approach - especially having a state for being uncertain whether something is nullable or not... having an operator embeded fallback approach also seems to be a lot more usable for the developer.

Also, this is an aside, but is your thing named after Snake Plissken?