无法将类型“ NSTaggedPointerString”的值强制转换为“ NSDictionary”

Question

启动我的应用程序时，出现红色错误：线程1：信号SIGABRT ，并且在分析中说：无法将类型'NSTaggedPointerString'（0x10dc70598）的值强制转换为'NSDictionary'（ 0x10dc708b8）。 代码：

func fetchDataFromServer(callback: @escaping (Room) -> ()) {
    DataService.dataService.ROOM_REF.observe(.childAdded) { (snapshot) in

        print("FOUND ROOM "+snapshot.key)

        let room = Room(key: snapshot.key, snapshot: snapshot.value as! Dictionary<String, AnyObject>)
        callback(room)
    }

一些JSON：

{
  "rooms" : {
    "-LRjiSQjXY4OkfQLRpCZ" : {
      "caption" : "Potatis",
      "thumbnailUrlFromStorage" : "gs://ilapp-   a1429.appspot.com/KLabp9zlfgZZ78dPQ9Eysrc9C6r2/564386764"
},