我在 Flutter Firebase 数据库中崩溃了，这是 crashlytics 上的崩溃日志
致命异常：NSInvalidArgumentException *** -[__NSPlaceholderDictionary initWithObjects:forKeys:count:]：尝试从对象 [1] 中插入 nil 对象
致命异常：NSInvalidArgumentException
0 CoreFoundation 0x19f11098c __exceptionPreprocess
1 libobjc.A.dylib 0x19ee390a4 objc_exception_throw
2 CoreFoundation 0x19f1663f8 -[__NSCFString characterAtIndex:].cold.1
3 CoreFoundation 0x19f16f75c -[__NSPlaceholderDictionary initWithObjects:forKeys:count:].cold.5
4 CoreFoundation 0x19effd5dc -[__NSPlaceholderDictionary initWithObjects:forKeys:count:]
5 CoreFoundation 0x19efef470 +[NSDictionary dictionaryWithObjects:forKeys:count:]
6 Runner 0x104e69a44 __53-[FLTFirebaseDatabasePlugin handleMethodCall:result:]_block_invoke.437 + 292 (FLTFirebaseDatabasePlugin.m:292)
7 Runner 0x104d469bc __39-[FRepo abortTransactionsAtNode:error:]_block_invoke + 1426 (FRepo.m:1426)
8 libdispatch.dylib 0x19eddd610 _dispatch_call_block_and_release
9 libdispatch.dylib 0x19edde184 _dispatch_client_callout
10 libdispatch.dylib 0x19ed901d0 _dispatch_main_queue_callback_4CF$VARIANT$mp
11 CoreFoundation 0x19f08e3c4 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__
12 CoreFoundation 0x19f0893b8 __CFRunLoopRun
13 CoreFoundation 0x19f0888bc CFRunLoopRunSpecific
14 GraphicsServices 0x1a8ef4328 GSEventRunModal
15 UIKitCore 0x1a311e6d4 UIApplicationMain
16 Runner 0x104cb0e58 main + 8 (AppDelegate.swift:8)
17 libdyld.dylib
0x19ef13460 start
崩溃：com.twitter.crashlytics.ios.exception SIGABRT ABORT 0x000000019ef08ebc
崩溃：com.twitter.crashlytics.ios.exception
0 Runner 0x104cca6bc CLSProcessRecordAllThreads + 4329924284
1 Runner 0x104ccaaa4 CLSProcessRecordAllThreads + 4329925284
2 Runner 0x104cba310 CLSHandler + 4329857808
3 Runner 0x104cc8cb4 __CLSExceptionRecord_block_invoke + 4329917620
4 libdispatch.dylib 0x19edde184 _dispatch_client_callout + 16
5 libdispatch.dylib 0x19ed90c44 _dispatch_lane_barrier_sync_invoke_and_complete + 56
6 Runner 0x104cc8720 CLSExceptionRecord + 4329916192
7 Runner 0x104cc854c CLSExceptionRecordNSException + 4329915724
8 Runner 0x104cc8140 CLSTerminateHandler() + 4329914688
9 libc++abi.dylib 0x19eede304 std::__terminate(void (*)()) + 16
10 libc++abi.dylib 0x19eede29c std::terminate() + 44
11 libobjc.A.dylib 0x19ee392dc _objc_terminate() + 10
12 libdispatch.dylib 0x19edde198 _dispatch_client_callout + 36
13 libdispatch.dylib 0x19ed901d0 _dispatch_main_queue_callback_4CF$VARIANT$mp + 1044
14 CoreFoundation 0x19f08e3c4 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 12
15 CoreFoundation 0x19f0893b8 __CFRunLoopRun + 2004
16 CoreFoundation 0x19f0888bc CFRunLoopRunSpecific + 464
17 GraphicsServices 0x1a8ef4328 GSEventRunModal + 104
18 UIKitCore 0x1a311e6d4 UIApplicationMain + 1936
19 Runner 0x104cb0e58 main + 8 (AppDelegate.swift:8)
20 libdyld.dylib 0x19ef13460 start + 4