FavoriteAuthorAge.kt

class FavoriteAuthor(_name: String, _lastname: String, _age: Int) {
    var name = _name
    var lastname = _lastname
    var age: Int? = _age
        get() {
            return if (field!! > 0) field else null
        }
}

  val favoriteauthor = FavoriteAuthor("Franz","Kafka",-1)
    println("Favorite Author: ${favoriteauthor.name} ${favoriteauthor.lastname} ${favoriteauthor.age}")
// Favorite Author: Franz Kafka null