这段程序会输出什么？

fun main() {
    var fallbackCalls = 0
    fun fallback(): String {
        fallbackCalls += 1
        return "guest"
    }

    val present: String? = "Ada"
    val absent: String? = null

    println(present?.uppercase() ?: fallback())
    println(absent?.uppercase() ?: fallback())
    println(fallbackCalls)
}