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:         isSystemIsolate: false,
        );
        var request = rpcRequest("setVMTimelineFlags", params: {
          'isolateId': isolate.id,
          // Note: the dynamic list below is intentional in order to exercise the
          // code under test.
          'recordedStreams': <dynamic>['GC', 'Dart', 'Embedder'],
        });
        var response = Success();
        when(serviceMock.getIsolate(isolate.id))
            .thenAnswer((Invocation invocation) {
          expect(invocation.namedArguments,
              equals({Symbol('isolateId'): null, Symbol('args'): null}));
  
negative.code:         breakpoints: [],
          isSystemIsolate: false,
        );
        var request =
            rpcRequest("getIsolate", params: {'isolateId': isolate.id!});
        when(serviceMock.getIsolate(isolate.id!))
            .thenAnswer((Invocation invocation) {
          expect(invocation.positionalArguments, equals([isolate.id]));
          return Future.value(isolate);
  