You can still use a null, however the point being made here is that null was failed to be included at type level.

See these for reference

* https://kotlinlang.org/docs/null-safety.html

* https://dart.dev/null-safety

* https://docs.microsoft.com/en-us/dotnet/csharp/nullable-refe...

An orthogonal approach would be using a data type such as Maybe or Option, but ergonomics depends on language.