anchor.diff:  class IsolateState {
     IsolateState(this.isolateRef);
   
  -  ValueListenable<bool> get isPaused => _isPaused;
  +  ValueListenable<bool?> get isPaused => _isPaused;
   
     final IsolateRef isolateRef;
   
  -  Future<Isolate> get isolate => _isolate.future;
  -  Completer<Isolate> _isolate = Completer();
  +  Future<Isolate?> get isolate => _completer.future;
  +  Completer<Isolate?> _completer = Completer();
   
  -  Isolate get isolateNow => _isolateNow;
  -  Isolate _isolateNow;
  +  Isolate? get isolateNow => _isolateNow;
  +  Isolate? _isolateNow;
   
     /// Paused is null until we know whether the isolate is paused or not.
  -  final _isPaused = ValueNotifier<bool>(null);
  +  final _isPaused = ValueNotifier<bool?>(null);
   
     void onIsolateLoaded(Isolate isolate) {
       _isolateNow = isolate;
  -    _isolate.complete(isolate);
  +    _completer.complete(isolate);
       if (_isPaused.value == null) {
         if (isolate.pauseEvent != null &&
  -          isolate.pauseEvent.kind != EventKind.kResume) {
  +          isolate.pauseEvent!.kind != EventKind.kResume) {
           _isPaused.value = true;
         } else {
           _isPaused.value = false;
  
positive.code: // Copyright 2018 The Chromium Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  // @dart=2.9
  
  import 'dart:async';
  import 'dart:core';
  
negative.code: 
    void dispose() {
      _isolateNow = null;
      if (!_completer.isCompleted) {
        _completer.complete(null);
      } else {
        _completer = Completer()..complete(null);
      }
    }
  
    void handleDebugEvent(String? kind) {
      switch (kind) {
        case EventKind.kResume:
          _isPaused.value = false;
  