package main

data class User(var email: String)

fun emailOrMissing(user: User?): String {
    if (user == null) { return "missing" }
    return user.email
}

fun optionalEmail(user: User?): String? {
    return user?.email
}

fun main() {
    val user: User? = User("user@example.com")
    println(emailOrMissing(user))
    println(user!!.email)
}