[IOS] Input chinese error

[suntianjun]

flutter_quill: ^6.3.5
ios

when input chinese by iphone‘s keyboard, the chinese words not showed on the text panel and error occured below:

The following _CastError was thrown during method call TextInputClient.updateEditingState:
type 'Null' is not a subtype of type 'Block' in type cast

When the exception was thrown, this was the stack:
#0 Document.queryChild (package:flutter_quill/src/models/documents/document.dart:185:28)
#1 Document.collectStyle (package:flutter_quill/src/models/documents/document.dart:156:17)
#2 QuillController.getSelectionStyle (package:flutter_quill/src/widgets/controller.dart:101:10)
#3 QuillController.replaceText (package:flutter_quill/src/widgets/controller.dart:222:21)
#4 RawEditorStateTextInputClientMixin.updateEditingValue (package:flutter_quill/src/widgets/raw_editor/raw_editor_state_text_input_client_mixin.dart:156:25)
#5 TextInput._updateEditingValue (package:flutter/src/services/text_input.dart:2029:43)
#6 TextInput._handleTextInputInvocation (package:flutter/src/services/text_input.dart:1854:29)
#7 TextInput._loudlyHandleTextInputInvocation (package:flutter/src/services/text_input.dart:1753:20)
#8 MethodChannel._handleAsMethodCall (package:flutter/src/services/platform_channel.dart:555:55)
#9 MethodChannel.setMethodCallHandler. (package:flutter/src/services/platform_channel.dart:548:34)
#10 _DefaultBinaryMessenger.setMessageHandler. (package:flutter/src/services/binding.dart:393:35)
#11 _invoke2 (dart:ui/hooks.dart:183:13)
#12 _ChannelCallbackRecord.invoke (dart:ui/channel_buffers.dart:40:5)
#13 _Channel.push (dart:ui/channel_buffers.dart:130:31)
#14 ChannelBuffers.push (dart:ui/channel_buffers.dart:326:17)
#15 PlatformDispatcher._dispatchPlatformMessage (dart:ui/platform_dispatcher.dart:664:22)
#16 _dispatchPlatformMessage (dart:ui/hooks.dart:86:31)
call: MethodCall(TextInputClient.updateEditingState, [2, {selectionBase: 2, composingExtent: 2, selectionAffinity: TextAffinity.downstream, text: 记录
, selectionIsDirectional: false, selectionExtent: 2, composingBase: 0}])