The role of "Nothing" when dealing with generics and its use

RoleOfNothing.kt

interface Base<out A> {
    fun someMethod(operation: (A) -> String): String
}

class Impl1<A>(val a: A): Base<A> { // could be a none empty node in linked list

    override fun someMethod(operation: (A) -> String): String {
        return "impl1 hahaha ${operation.invoke(a)}"
    }

}

class Impl2: Base<Nothing> { // could be an empty node in linked list

    override fun someMethod(operation: (Nothing) -> String): String {
        return "impl2 hahaha NOTHING"
    }

}

/**
 * Terminal output:
 * $ impl1 hahaha 0
 * $ impl2 hahaha NOTHING
 */
fun main() {
    val interface1: Base<Int> = Impl1<Int>(0) //intentionally verbose
    val interface2: Base<Int> = Impl2()

    interface1.someMethod { it.toString() }.also { println(it) }
    interface2.someMethod { it.toString() }.also { println(it) }
}