Multi-key sort of nullable records with compareBy

data class User(val name: String, val age: Int?, val joined: Long)

fun sortUsers(users: List<User>): List<User> = users.sortedWith(
    compareBy<User> { it.age == null }
        .thenBy { it.age ?: Int.MAX_VALUE }
        .thenByDescending { it.joined }
        .thenBy { it.name.lowercase() }
)

val users = listOf(User("bo", null, 2), User("al", 30, 1))
// al first, then bo (null age sorts last)
check(sortUsers(users).map { it.name } == listOf("al", "bo"))