internal class A<T> {
    fun foo(nonMutableCollection: Collection<String?>?,
            mutableCollection: MutableCollection<String?>,
            mutableSet: MutableSet<T?>,
            mutableMap: MutableMap<String?, T>) {
        mutableCollection.addAll(nonMutableCollection!!)
        mutableSet.add(mutableMap.remove("a"))
    }
}