Thank you for your compliment. I appreciate your feedback.

You are very right. For example, here is another interesting point related to Nothing being the subclass of all classes. This sealed class will not compile

sealed class LinkedList<T>  {

    data class Node<T>(val payload: T, var next: LinkedList<T> = EmptyList) : LinkedList<T>()

    object EmptyList : LinkedList<Nothing>()

}

The out variance modifier is missing. The compiler complains that the default value of next cannot be set. We cannot write

var next: LinkedList<T> = EmptyList

unless we write

sealed class LinkedList<out T>