找出配送状态标签里的 bug

sealed interface DeliveryState {
    data object Queued : DeliveryState
    data object Sent : DeliveryState
    data class Failed(val reason: String) : DeliveryState
}

fun label(state: DeliveryState): String = when (state) {
    DeliveryState.Queued -> "queued"
    DeliveryState.Sent -> "sent"
    else -> "unknown"
}

fun main() {
    println(label(DeliveryState.Failed("offline")))
}