[equalsione]

I’m not familiar enough with kotlin to comment fully but from your description the checker framework [0] appears to do the same thing in Java.

I confess I’m not fond of checker framework. I find the error messages can be obtuse but it is very effective.

0 - https://checkerframework.org/

[a57721]

Kotlin supports nullability on the level of the type system, it is similar to TypeScript in this respect.

The problem with nullability annotations in Java is that they are not enforced, and there is no commonly adopted standard. There are like ten competing libraries with similar annotations. There was JSR 305 ("Annotations for Software Defect Detection"), but it has been dormant. When you import a third party library, you never know what kind of nullability annotations it uses and if it uses them at all.