I don't know Kotlin, but these usually are distinct from Options in an important way, idempotency `String?? = String?` or `String|null|null = String|null`.

This equation makes sense for some mental models, but isn't quite the same as Option. In particular, Option[T] has the nice property that you can map over its inner type in a naive fashion `forall S. (T -> S) -> (Option[T] -> Option[S])` whereas the coalescing version above needs an additional assumption that `S` is non-nullable.

    forall S not null. (T -> S) -> (T? -> S?)

This can really get in the way of some kinds of generic programming.