Any time you see things like `Type!` or `(Mutable)...

# tornadofx

[Ruckus]

Any time you see things like Type! or (Mutable)Collection<Type!>! or Array<(out) Type!>!, those are types that were sent if from interoperation with other languages, and so Kotlin can't tell you for sure if the type is nullable, mutable, or variant, and lets you handle it instead.