anchor.diff:  }
   
   Map<String, Object> rpcRequest(String method,
  -        {Map<String, Object> params = const {}, String id = "1"}) =>
  +        {Map<String, Object>? params = const {}, String id = "1"}) =>
       {
         "jsonrpc": "2.0",
         "method": method,
  -      "params": params,
  +      if (params != null) "params": params,
         "id": id,
       };
   
  
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:       var responseQueue = StreamQueue(responsesController.stream);
  
        var clientInputController =
            StreamController<Map<String, Object?>>.broadcast();
        var clientOutputController =
            StreamController<Map<String, Object>>.broadcast();
        var client = VmService(
            clientInputController.stream.map(jsonEncode),
            (String message) => clientOutputController
                .add(jsonDecode(message).cast<String, Object>()),
            disposeHandler: () async {
          await clientInputController.close();
          await clientOutputController.close();
  