A modern programming language that makes developers happier.

kotlinlang

Suppose some java dependency declares an interface:

```
public interface JavaIFace {
    void f(String s);
}
```

A kotlin usage (seperate module) is unsure of nullability, so the clever developer assumes it’s nullable
```
class KotlinImpl : JavaIFace {
    override fun f(s: String?) {}
}
```

If the library now adds `@NotNull` to the argument, `KotlinImpl::f` overrides nothing and fails to compile now. Correct? This change breaks source compatibility for library author