anchor.diff:          // Connect another client to get the previous register events and the
           // unregister event.
           var requestsController2 = StreamController<Map<String, Object>>();
  -        var responsesController2 = StreamController<Map<String, Object>>();
  +        var responsesController2 = StreamController<Map<String, Object?>>();
           addTearDown(() {
             requestsController2.close();
             responsesController2.close();
  
positive.code:         requestsController.add(request);
          await expectLater(responseQueue, emitsThrough(rpcResponse(response)));
  
          eventController = serviceMock.streamControllers[streamId];
  
          var events = [
            Event(
  
negative.code: import 'package:vm_service/vm_service.dart';
  
  void main() {
    late MockVmService serviceMock;
    late StreamController<Map<String, Object>> requestsController;
    late StreamController<Map<String, Object?>> responsesController;
    late ServiceExtensionRegistry serviceRegistry;
  
    setUp(() {
      serviceMock = MockVmService();
      requestsController = StreamController<Map<String, Object>>();
      responsesController = StreamController<Map<String, Object?>>();
      serviceRegistry = ServiceExtensionRegistry();
      VmServerConnection(requestsController.stream, responsesController.sink,
          serviceRegistry, serviceMock);
  