Why can't I set `foo` of `b: Base<*>` to `null`? I understand why it can't be set to any list ...

# getting-started

[Lukellmann]

Why can't I set foo of b: Base<*> to null? I understand why it can't be set to any list but don't get why null shouldn't be allowed.

abstract class Base<T> {
    // foo is nullable
    final var foo: MutableList<T>? = mutableListOf()
}

class Inherit : Base<String>()

val a = Inherit()
a.foo = null // works
a.foo = mutableListOf() // works

val b: Any = if (Random.nextBoolean()) a else Any()
if (b is Base<*>) {
    // error: 'Setter for 'foo' is removed by type projection'
    // I understand why it can't be set to any list but `null` should always be ok
    b.foo = null
}

[dmitriy.novozhilov]

Actually, it looks like a bug or new minor feature
Please report it to kotl.in/issue

[Lukellmann]

https://youtrack.jetbrains.com/issue/KT-51045