Ios persistenceEnabled=false时，Firebase runTransactionBlock不工作

我试图使用runTransaction块更新对象计数，但返回的FIRMutable数据始终为（null）

如果我在FirebaseDatabase上启用持久性，它会工作，但我不想启用它

let artworkRef = FIRDatabase.database().reference().child(doodlesKey).child(artwork.uid)
artworkRef.runTransactionBlock { (mutableData) -> FIRTransactionResult in
    if var artworkData = mutableData.value as? [String: AnyObject] {
        var bookmarkCount = artworkData["bookmarkCount"] as? Int ?? 0
        bookmarkCount += 1
        artworkData["bookmarkCount"] = bookmarkCount
        mutableData.value = artworkData
        return FIRTransactionResult.successWithValue(mutableData)
    }
    return FIRTransactionResult.successWithValue(mutableData)
}