(I don't want to use a sealed class for just this emptiness case)

Personally I'd recommend it. Why don't you want to?

hrm... have to think about that

I agree, but it's important to remember that Kotlin is a null-safe language, not a non-null language (like Rust). If the problem at hand has a clear use case for missing/empty/optional values, nullability is the way to go, and Kotlin's language features make it pleasant and safe to do so.

ok, thanks for the detailed explanation - that was helpful! I'll probably wrap my head around making the thing nullable then.