Actually in Kotlin, nullability is part of the type system and denoted with a ?. So String and String? are two different types. Dereferencing a nullable type is a compile error until you do the null check. Doing that triggers a smart cast to the non nulled type. So the inferred type becomes non nullable and you don't have to do any casts. You can force this cast by using the operator !!, which you should avoid for obvious reasons but is useful with some legacy code. If you get this wrong you still get an npe.

It also provides backward compatibility with java where java types are considered nullable by default unless other wise annotated with a @NonNull. Also you get nice warnings about redundant null checks.

This provides for a lot of extra compile time safety and it largely removes the need for Maybe, Optional, and other kludges that people have been coming up with to force programmers to replace null checks with empty checks.