diff --git a/android/build.gradle b/android/build.gradle
index 54face2..32aa8e4 100644
--- a/android/build.gradle
+++ b/android/build.gradle
@@ -2,16 +2,16 @@ group 'com.tugberka.mdsflutter'
 version '1.0-SNAPSHOT'
 
 buildscript {
-    ext.kotlin_version = '1.3.50'
+    ext.kotlin_version = '1.5.31'
     repositories {
         google()
         jcenter()
     }
 
     dependencies {
-        classpath 'com.android.tools.build:gradle:3.5.0'
+        classpath 'com.android.tools.build:gradle:7.0.2'
         classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
-        classpath 'com.google.protobuf:protobuf-gradle-plugin:0.8.10'
+        classpath 'com.google.protobuf:protobuf-gradle-plugin:0.8.15'
     }
 }
 
@@ -49,26 +49,37 @@ protobuf {
     // Configure the protoc executable
     protoc {
         // Download from repositories
-        artifact = 'com.google.protobuf:protoc:3.9.1'
+        // artifact = 'com.google.protobuf:protoc:3.9.1'
+        artifact = 'com.google.protobuf:protoc:3.17.3'
     }
-    plugins {
+  /*   plugins {
         javalite {
             // The codegen for lite comes as a separate artifact
             artifact = 'com.google.protobuf:protoc-gen-javalite:3.0.0'
         }
-    }
-    generateProtoTasks {
+    } */
+   /*  generateProtoTasks {
         all().each { task ->
             task.plugins {
                 javalite { }
             }
         }
+    } */
+       generateProtoTasks {
+        all().each { task ->
+            task.builtins {
+                java {
+                    option "lite"
+                }
+            }
+        }
     }
 }
 
 dependencies {
     implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
-    implementation 'com.google.protobuf:protobuf-lite:3.0.1'
+    //implementation 'com.google.protobuf:protobuf-lite:3.0.1'
+    implementation 'com.google.protobuf:protobuf-javalite:3.17.3'
     // RxAndroidBle helper library
     implementation "com.polidea.rxandroidble2:rxandroidble:1.11.0"
     implementation(name: 'mdslib', version: '+', ext: 'aar')
diff --git a/android/gradle/wrapper/gradle-wrapper.properties b/android/gradle/wrapper/gradle-wrapper.properties
index 01a286e..297f2fe 100644
--- a/android/gradle/wrapper/gradle-wrapper.properties
+++ b/android/gradle/wrapper/gradle-wrapper.properties
@@ -2,4 +2,4 @@ distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-5.6.2-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-7.0.2-all.zip
diff --git a/example/lib/AppModel.dart b/example/lib/AppModel.dart
index 479af8a..f69ca9e 100644
--- a/example/lib/AppModel.dart
+++ b/example/lib/AppModel.dart
@@ -1,4 +1,3 @@
-
 import 'dart:collection';
 import 'dart:convert';
 
@@ -11,13 +10,13 @@ import 'package:mdsflutter_example/DeviceConnectionStatus.dart';
 import 'dart:developer' as developer;
 
 class AppModel extends ChangeNotifier {
-
-  final Set<Device> _deviceList = Set();
+  final Set<Device?> _deviceList = Set();
   bool _isScanning = false;
-  void Function(Device) _onDeviceMdsConnectedCb;
-  void Function(Device) _onDeviceDisonnectedCb;
+  void Function(Device)? _onDeviceMdsConnectedCb;
+  void Function(Device)? _onDeviceDisonnectedCb;
 
-  UnmodifiableListView<Device> get deviceList => UnmodifiableListView(_deviceList);
+  UnmodifiableListView<Device?> get deviceList =>
+      UnmodifiableListView(_deviceList);
 
   bool get isScanning => _isScanning;
 
@@ -33,7 +32,8 @@ class AppModel extends ChangeNotifier {
 
   void startScan() {
     _deviceList.forEach((device) {
-      if (device.connectionStatus == DeviceConnectionStatus.CONNECTED) {
+      if (device != null &&
+          device.connectionStatus == DeviceConnectionStatus.CONNECTED) {
         disconnectFromDevice(device);
       }
     });
@@ -43,7 +43,7 @@ class AppModel extends ChangeNotifier {
 
     try {
       Mds.startScan((name, address) {
-        Device device = Device(name, address);
+        Device device = Device(name ?? "", address ?? "");
         if (!_deviceList.contains(device)) {
           _deviceList.add(device);
           notifyListeners();
@@ -65,36 +65,42 @@ class AppModel extends ChangeNotifier {
 
   void connectToDevice(Device device) {
     device.onConnecting();
-    Mds.connect(device.address,
-            (serial) => _onDeviceMdsConnected(device.address, serial),
-            () => _onDeviceDisconnected(device.address),
-            () => _onDeviceConnectError(device.address)
-    );
+    final address = device.address;
+    if (address == null) return;
+    Mds.connect(
+        address,
+        (serial) => _onDeviceMdsConnected(address, serial),
+        () => _onDeviceDisconnected(address),
+        () => _onDeviceConnectError(address));
   }
 
   void disconnectFromDevice(Device device) {
-    Mds.disconnect(device.address);
-    _onDeviceDisconnected(device.address);
+    final address = device.address;
+    if (address == null) return;
+    Mds.disconnect(address);
+    _onDeviceDisconnected(address);
   }
 
   void _onDeviceMdsConnected(String address, String serial) {
-    Device foundDevice = _deviceList.firstWhere((element) => element.address == address);
+    Device? foundDevice =
+        _deviceList.firstWhere((element) => element?.address == address);
     if (foundDevice != null) {
       foundDevice.onMdsConnected(serial);
       notifyListeners();
       if (_onDeviceMdsConnectedCb != null) {
-        _onDeviceMdsConnectedCb.call(foundDevice);
+        _onDeviceMdsConnectedCb?.call(foundDevice);
       }
     }
   }
 
   void _onDeviceDisconnected(String address) {
-    Device foundDevice = _deviceList.firstWhere((element) => element.address == address);
+    Device? foundDevice =
+        _deviceList.firstWhere((element) => element?.address == address);
     if (foundDevice != null) {
       foundDevice.onDisconnected();
       notifyListeners();
       if (_onDeviceDisonnectedCb != null) {
-        _onDeviceDisonnectedCb.call(foundDevice);
+        _onDeviceDisonnectedCb?.call(foundDevice);
       }
     }
   }
@@ -102,4 +108,4 @@ class AppModel extends ChangeNotifier {
   void _onDeviceConnectError(String address) {
     _onDeviceDisconnected(address);
   }
-}
\ No newline at end of file
+}
diff --git a/example/lib/Device.dart b/example/lib/Device.dart
index 73d5c5d..c1f2d38 100644
--- a/example/lib/Device.dart
+++ b/example/lib/Device.dart
@@ -1,21 +1,21 @@
-
 import 'package:mdsflutter_example/DeviceConnectionStatus.dart';
 import 'package:mdsflutter_example/DeviceModel.dart';
 
 class Device {
-  String _address;
-  String _name;
-  String _serial;
-  DeviceConnectionStatus _connectionStatus = DeviceConnectionStatus.NOT_CONNECTED;
+  String? _address;
+  String? _name;
+  String? _serial;
+  DeviceConnectionStatus _connectionStatus =
+      DeviceConnectionStatus.NOT_CONNECTED;
 
   Device(String name, String address) {
     _name = name;
     _address = address;
   }
 
-  String get name => _name != null ? _name : "";
-  String get address => _address != null ? _address : "";
-  String get serial => _serial != null ? _serial : "";
+  String? get name => _name != null ? _name : "";
+  String? get address => _address != null ? _address : "";
+  String? get serial => _serial != null ? _serial : "";
   DeviceConnectionStatus get connectionStatus => _connectionStatus;
 
   void onConnecting() => _connectionStatus = DeviceConnectionStatus.CONNECTING;
@@ -23,8 +23,11 @@ class Device {
     _serial = serial;
     _connectionStatus = DeviceConnectionStatus.CONNECTED;
   }
-  void onDisconnected() => _connectionStatus = DeviceConnectionStatus.NOT_CONNECTED;
 
-  bool operator ==(o) => o is Device && o._address == _address && o._name == _name;
+  void onDisconnected() =>
+      _connectionStatus = DeviceConnectionStatus.NOT_CONNECTED;
+
+  bool operator ==(o) =>
+      o is Device && o._address == _address && o._name == _name;
   int get hashCode => _address.hashCode * _name.hashCode;
-}
\ No newline at end of file
+}
diff --git a/example/lib/DeviceInteractionWidget.dart b/example/lib/DeviceInteractionWidget.dart
index 71a8edb..95dff08 100644
--- a/example/lib/DeviceInteractionWidget.dart
+++ b/example/lib/DeviceInteractionWidget.dart
@@ -18,13 +18,13 @@ class DeviceInteractionWidget extends StatefulWidget {
 }
 
 class _DeviceInteractionWidgetState extends State<DeviceInteractionWidget> {
-  AppModel _appModel;
+  AppModel? _appModel;
 
   @override
   void initState() {
     super.initState();
     _appModel = Provider.of<AppModel>(context, listen: false);
-    _appModel.onDeviceMdsDisconnected((device) => { Navigator.pop(context) });
+    _appModel?.onDeviceMdsDisconnected((device) => {Navigator.pop(context)});
   }
 
   void _onAccelerometerButtonPressed(DeviceModel deviceModel) {
@@ -45,7 +45,7 @@ class _DeviceInteractionWidgetState extends State<DeviceInteractionWidget> {
 
   @override
   void dispose() {
-    _appModel.disconnectFromDevice(widget.device);
+    _appModel?.disconnectFromDevice(widget.device);
     super.dispose();
   }
 
@@ -53,12 +53,12 @@ class _DeviceInteractionWidgetState extends State<DeviceInteractionWidget> {
   Widget build(BuildContext context) {
     Device device = widget.device;
     return ChangeNotifierProvider(
-      create: (context) => DeviceModel(device.name, device.serial),
+      create: (context) => DeviceModel(device.name ?? "", device.serial ?? ""),
       child: Consumer<DeviceModel>(
         builder: (context, model, child) {
           return Scaffold(
               appBar: AppBar(
-                title: Text(device.name),
+                title: Text(device.name ?? ""),
               ),
               body: Column(
                 mainAxisSize: MainAxisSize.min,
@@ -68,8 +68,7 @@ class _DeviceInteractionWidgetState extends State<DeviceInteractionWidget> {
                   _ledItem(model),
                   _temperatureItem(model)
                 ],
-              )
-          );
+              ));
         },
       ),
     );
@@ -80,8 +79,10 @@ class _DeviceInteractionWidgetState extends State<DeviceInteractionWidget> {
       child: ListTile(
         title: Text("Accelerometer"),
         subtitle: Text(deviceModel.accelerometerData),
-        trailing: RaisedButton(
-          child: Text(deviceModel.accelerometerSubscribed ? "Unsubscribe" : "Subscribe"),
+        trailing: ElevatedButton(
+          child: Text(deviceModel.accelerometerSubscribed
+              ? "Unsubscribe"
+              : "Subscribe"),
           onPressed: () => _onAccelerometerButtonPressed(deviceModel),
         ),
       ),
@@ -93,7 +94,7 @@ class _DeviceInteractionWidgetState extends State<DeviceInteractionWidget> {
       child: ListTile(
         title: Text("Heart rate"),
         subtitle: Text(deviceModel.hrData),
-        trailing: RaisedButton(
+        trailing: ElevatedButton(
           child: Text(deviceModel.hrSubscribed ? "Unsubscribe" : "Subscribe"),
           onPressed: () => _onHrButtonPressed(deviceModel),
         ),
@@ -107,7 +108,7 @@ class _DeviceInteractionWidgetState extends State<DeviceInteractionWidget> {
         title: Text("Led"),
         trailing: Switch(
           value: deviceModel.ledStatus,
-          onChanged: (b) => { deviceModel.switchLed() },
+          onChanged: (b) => {deviceModel.switchLed()},
         ),
       ),
     );
@@ -118,11 +119,11 @@ class _DeviceInteractionWidgetState extends State<DeviceInteractionWidget> {
       child: ListTile(
         title: Text("Temperature"),
         subtitle: Text(deviceModel.temperature),
-        trailing: RaisedButton(
+        trailing: ElevatedButton(
           child: Text("Get"),
           onPressed: () => deviceModel.getTemperature(),
         ),
       ),
     );
   }
-}
\ No newline at end of file
+}
diff --git a/example/lib/DeviceModel.dart b/example/lib/DeviceModel.dart
index 9589df1..d96392a 100644
--- a/example/lib/DeviceModel.dart
+++ b/example/lib/DeviceModel.dart
@@ -12,12 +12,12 @@ class DeviceModel extends ChangeNotifier {
   String get name => _name;
   String get serial => _serial;
 
-  int _accSubscription;
+  int? _accSubscription;
   String _accelerometerData = "";
   String get accelerometerData => _accelerometerData;
   bool get accelerometerSubscribed => _accSubscription != null;
 
-  int _hrSubscription;
+  int? _hrSubscription;
   String _hrData = "";
   String get hrData => _hrData;
   bool get hrSubscribed => _hrSubscription != null;
@@ -38,8 +38,7 @@ class DeviceModel extends ChangeNotifier {
         (d, c) => {},
         (e, c) => {},
         (data) => _onNewAccelerometerData(data),
-        (e, c) => {}
-    );
+        (e, c) => {});
     notifyListeners();
   }
 
@@ -48,12 +47,18 @@ class DeviceModel extends ChangeNotifier {
     Map<String, dynamic> body = accData["Body"];
     List<dynamic> accArray = body["ArrayAcc"];
     dynamic acc = accArray.last;
-    _accelerometerData = "x: " + acc["x"].toStringAsFixed(2) + "\ny: " + acc["y"].toStringAsFixed(2) + "\nz: " + acc["z"].toStringAsFixed(2);
+    _accelerometerData = "x: " +
+        acc["x"].toStringAsFixed(2) +
+        "\ny: " +
+        acc["y"].toStringAsFixed(2) +
+        "\nz: " +
+        acc["z"].toStringAsFixed(2);
     notifyListeners();
   }
 
   void unsubscribeFromAccelerometer() {
-    Mds.unsubscribe(_accSubscription);
+    if (_accSubscription == null) return;
+    Mds.unsubscribe(_accSubscription!);
     _accSubscription = null;
     notifyListeners();
   }
@@ -61,13 +66,12 @@ class DeviceModel extends ChangeNotifier {
   void subscribeToHr() {
     _hrData = "";
     _hrSubscription = Mds.subscribe(
-      Mds.createSubscriptionUri(_serial, "/Meas/HR"),
-      "{}",
-      (d, c) => {},
-      (e, c) => {},
-      (data) => _onNewHrData(data),
-      (e, c) => {}
-    );
+        Mds.createSubscriptionUri(_serial, "/Meas/HR"),
+        "{}",
+        (d, c) => {},
+        (e, c) => {},
+        (data) => _onNewHrData(data),
+        (e, c) => {});
     notifyListeners();
   }
 
@@ -80,7 +84,8 @@ class DeviceModel extends ChangeNotifier {
   }
 
   void unsubscribeFromHr() {
-    Mds.unsubscribe(_hrSubscription);
+    if (_hrSubscription == null) return;
+    Mds.unsubscribe(_hrSubscription!);
     _hrSubscription = null;
     notifyListeners();
   }
@@ -89,27 +94,19 @@ class DeviceModel extends ChangeNotifier {
     Map<String, bool> contract = new Map<String, bool>();
     contract["isOn"] = !_ledStatus;
     Mds.put(
-      Mds.createRequestUri(_serial, "/Component/Led"),
-        jsonEncode(contract),
-            (data, code) {
-          _ledStatus = !_ledStatus;
-          notifyListeners();
-        },
-            (e, c) => {}
-    );
+        Mds.createRequestUri(_serial, "/Component/Led"), jsonEncode(contract),
+        (data, code) {
+      _ledStatus = !_ledStatus;
+      notifyListeners();
+    }, (e, c) => {});
   }
 
   void getTemperature() {
-    Mds.get(
-        Mds.createRequestUri(_serial, "/Meas/Temp"),
-        "{}",
-            (data, code) {
-          double kelvin = jsonDecode(data)["Content"]["Measurement"];
-          double temperatureVal = kelvin - 274.15;
-          _temperature = temperatureVal.toStringAsFixed(1) + " C";
-          notifyListeners();
-        },
-            (e, c) => {}
-    );
+    Mds.get(Mds.createRequestUri(_serial, "/Meas/Temp"), "{}", (data, code) {
+      double kelvin = jsonDecode(data)["Content"]["Measurement"];
+      double temperatureVal = kelvin - 274.15;
+      _temperature = temperatureVal.toStringAsFixed(1) + " C";
+      notifyListeners();
+    }, (e, c) => {});
   }
-}
\ No newline at end of file
+}
diff --git a/example/lib/ScanWidget.dart b/example/lib/ScanWidget.dart
index 272d06e..07cd218 100644
--- a/example/lib/ScanWidget.dart
+++ b/example/lib/ScanWidget.dart
@@ -14,59 +14,61 @@ class ScanWidget extends StatefulWidget {
 }
 
 class _ScanWidgetState extends State<ScanWidget> {
-
-  AppModel model;
+  AppModel? model;
 
   @override
   void initState() {
     super.initState();
     initPlatformState();
     model = Provider.of<AppModel>(context, listen: false);
-    model.onDeviceMdsConnected((device) => {
-      Navigator.push(context, MaterialPageRoute(builder: (context) =>
-          DeviceInteractionWidget(device)
-      ))
-    });
+    model?.onDeviceMdsConnected((device) => {
+          Navigator.push(
+              context,
+              MaterialPageRoute(
+                  builder: (context) => DeviceInteractionWidget(device)))
+        });
   }
 
   Future<void> initPlatformState() async {
     if (!mounted) return;
 
     if (defaultTargetPlatform == TargetPlatform.android) {
-      Permission.locationWhenInUse.isUndetermined.then((value) =>
-          Permission.locationWhenInUse.request()
-      );
+      Permission.locationWhenInUse.isDenied
+          .then((value) => Permission.locationWhenInUse.request());
 
-      Permission.locationWhenInUse.isDenied.then((value) =>
-          Permission.locationWhenInUse.request()
-      );
+      Permission.locationWhenInUse.isDenied
+          .then((value) => Permission.locationWhenInUse.request());
     }
   }
 
   Widget _buildDeviceItem(BuildContext context, int index) {
     return Card(
       child: ListTile(
-        title: Text(model.deviceList[index].name),
-        subtitle: Text(model.deviceList[index].address),
-        trailing: Text(model.deviceList[index].connectionStatus.statusName),
-        onTap: () => model.connectToDevice(model.deviceList[index]),
+        title: Text(model?.deviceList[index]?.name ?? ""),
+        subtitle: Text(model?.deviceList[index]?.address ?? ""),
+        trailing:
+            Text(model?.deviceList[index]?.connectionStatus.statusName ?? ""),
+        onTap: () {
+          final device = model?.deviceList[index];
+          if (device != null) model?.connectToDevice(device);
+        },
       ),
     );
   }
 
-  Widget _buildDeviceList(List<Device> deviceList) {
-    return new Expanded(child: new ListView.builder(
-        itemCount: model.deviceList.length,
-        itemBuilder: (BuildContext context, int index) => _buildDeviceItem(context, index)
-    )
-    );
+  Widget _buildDeviceList(List<Device?> deviceList) {
+    return new Expanded(
+        child: new ListView.builder(
+            itemCount: model?.deviceList.length,
+            itemBuilder: (BuildContext context, int index) =>
+                _buildDeviceItem(context, index)));
   }
 
   void onScanButtonPressed() {
-    if (model.isScanning) {
-      model.stopScan();
+    if (model?.isScanning ?? false) {
+      model?.stopScan();
     } else {
-      model.startScan();
+      model?.startScan();
     }
   }
 
@@ -81,7 +83,7 @@ class _ScanWidgetState extends State<ScanWidget> {
             return Column(
               mainAxisSize: MainAxisSize.min,
               children: <Widget>[
-                RaisedButton(
+                ElevatedButton(
                   onPressed: onScanButtonPressed,
                   child: Text(model.scanButtonText),
                 ),
@@ -89,7 +91,6 @@ class _ScanWidgetState extends State<ScanWidget> {
               ],
             );
           },
-        )
-    );
+        ));
   }
 }
diff --git a/example/pubspec.yaml b/example/pubspec.yaml
index 165ec81..8abcb40 100644
--- a/example/pubspec.yaml
+++ b/example/pubspec.yaml
@@ -6,27 +6,22 @@ description: Demonstrates how to use the mdsflutter plugin.
 publish_to: 'none' # Remove this line if you wish to publish to pub.dev
 
 environment:
-  sdk: ">=2.7.0 <3.0.0"
+  sdk: ">=2.12.0 <3.0.0"
 
 dependencies:
   flutter:
     sdk: flutter
 
-  mdsflutter:
-    # When depending on this package from a real application you should use:
-    #   mdsflutter: ^x.y.z
-    # See https://dart.dev/tools/pub/dependencies#version-constraints
-    # The example app is bundled with the plugin so we use a path dependency on
-    # the parent directory to use the current plugin's version.
-    path: ../
+  mdsflutter: 
+    path: ../../mdsflutter
 
   # The following adds the Cupertino Icons font to your application.
   # Use with the CupertinoIcons class for iOS style icons.
-  cupertino_icons: ^0.1.3
+  cupertino_icons: ^1.0.3
 
-  provider: ^3.0.0
+  provider: ^6.0.1
 
-  permission_handler: ^5.0.1
+  permission_handler: ^8.2.2
 
 dev_dependencies:
   flutter_test:
diff --git a/lib/Mds.dart b/lib/Mds.dart
index 1aa186e..d27f32b 100644
--- a/lib/Mds.dart
+++ b/lib/Mds.dart
@@ -9,7 +9,7 @@ class Mds {
   /// devices will get UUID as the address parameter. Scanning is terminated
   /// automatically after 60 seconds. Only devices with Movesense services are
   /// returned.
-  static void startScan(void Function(String, String) onNewDeviceFound) {
+  static void startScan(void Function(String?, String?) onNewDeviceFound) {
     MdsImpl().startScan(onNewDeviceFound);
   }
 
@@ -27,10 +27,8 @@ class Mds {
   /// Note: If you need DeviceInfo upon connection, you should manually
   /// subscribe to "MDS/ConnectedDevices" to get detailed device information
   /// upon connection.
-  static void connect(String address,
-      void Function(String) onConnected,
-      void Function() onDisconnected,
-      void Function() onConnectionError) {
+  static void connect(String address, void Function(String) onConnected,
+      void Function() onDisconnected, void Function() onConnectionError) {
     MdsImpl().connect(address, onConnected, onDisconnected, onConnectionError);
   }
 
@@ -44,7 +42,8 @@ class Mds {
   /// request is successful, onSuccess is called with response data in json
   /// string format, and status code. Upon error, onError is called with reason
   /// and status code.
-  static void get(String uri,
+  static void get(
+      String uri,
       String contract,
       void Function(String, int) onSuccess,
       void Function(String, int) onError) {
@@ -56,7 +55,8 @@ class Mds {
   /// request is successful, onSuccess is called with response data in json
   /// string format, and status code. Upon error, onError is called with reason
   /// and status code.
-  static void put(String uri,
+  static void put(
+      String uri,
       String contract,
       void Function(String, int) onSuccess,
       void Function(String, int) onError) {
@@ -68,7 +68,8 @@ class Mds {
   /// request is successful, onSuccess is called with response data in json
   /// string format, and status code. Upon error, onError is called with reason
   /// and status code.
-  static void post(String uri,
+  static void post(
+      String uri,
       String contract,
       void Function(String, int) onSuccess,
       void Function(String, int) onError) {
@@ -80,7 +81,8 @@ class Mds {
   /// request is successful, onSuccess is called with response data in json
   /// string format, and status code. Upon error, onError is called with reason
   /// and status code.
-  static void del(String uri,
+  static void del(
+      String uri,
       String contract,
       void Function(String, int) onSuccess,
       void Function(String, int) onError) {
@@ -98,7 +100,8 @@ class Mds {
   ///
   /// This call returns a subscription id. It must be held and used when
   /// unsubscribing.
-  static int subscribe(String uri,
+  static int subscribe(
+      String uri,
       String contract,
       void Function(String, int) onSuccess,
       void Function(String, int) onError,
@@ -118,6 +121,6 @@ class Mds {
   }
 
   static String createSubscriptionUri(String serial, String resource) {
-    return  serial + resource;
+    return serial + resource;
   }
 }
diff --git a/lib/gen/protos/mdsflutter.pb.dart b/lib/gen/protos/mdsflutter.pb.dart
index f858f39..e70df27 100644
--- a/lib/gen/protos/mdsflutter.pb.dart
+++ b/lib/gen/protos/mdsflutter.pb.dart
@@ -2,7 +2,7 @@
 //  Generated code. Do not modify.
 //  source: protos/mdsflutter.proto
 //
-// @dart = 2.3
+
 // ignore_for_file: annotate_overrides,camel_case_types,unnecessary_const,non_constant_identifier_names,library_prefixes,unused_import,unused_shown_name,return_of_invalid_type
 
 import 'dart:core' as $core;
@@ -22,7 +22,7 @@ class RequestResult extends $pb.GeneratedMessage {
   factory RequestResult.fromBuffer($core.List<$core.int> i, [$pb.ExtensionRegistry r = $pb.ExtensionRegistry.EMPTY]) => create()..mergeFromBuffer(i, r);
   factory RequestResult.fromJson($core.String i, [$pb.ExtensionRegistry r = $pb.ExtensionRegistry.EMPTY]) => create()..mergeFromJson(i, r);
   RequestResult clone() => RequestResult()..mergeFromMessage(this);
-  RequestResult copyWith(void Function(RequestResult) updates) => super.copyWith((message) => updates(message as RequestResult));
+  RequestResult copyWith(void Function(RequestResult) updates) => super.copyWith((message) => updates(message as RequestResult)) as RequestResult;
   $pb.BuilderInfo get info_ => _i;
   @$core.pragma('dart2js:noInline')
   static RequestResult create() => RequestResult._();
@@ -30,7 +30,7 @@ class RequestResult extends $pb.GeneratedMessage {
   static $pb.PbList<RequestResult> createRepeated() => $pb.PbList<RequestResult>();
   @$core.pragma('dart2js:noInline')
   static RequestResult getDefault() => _defaultInstance ??= $pb.GeneratedMessage.$_defaultFor<RequestResult>(create);
-  static RequestResult _defaultInstance;
+  static RequestResult? _defaultInstance;
 
   @$pb.TagNumber(1)
   $core.int get requestId => $_getIZ(0);
@@ -73,7 +73,7 @@ class RequestError extends $pb.GeneratedMessage {
   factory RequestError.fromBuffer($core.List<$core.int> i, [$pb.ExtensionRegistry r = $pb.ExtensionRegistry.EMPTY]) => create()..mergeFromBuffer(i, r);
   factory RequestError.fromJson($core.String i, [$pb.ExtensionRegistry r = $pb.ExtensionRegistry.EMPTY]) => create()..mergeFromJson(i, r);
   RequestError clone() => RequestError()..mergeFromMessage(this);
-  RequestError copyWith(void Function(RequestError) updates) => super.copyWith((message) => updates(message as RequestError));
+  RequestError copyWith(void Function(RequestError) updates) => super.copyWith((message) => updates(message as RequestError)) as RequestError;
   $pb.BuilderInfo get info_ => _i;
   @$core.pragma('dart2js:noInline')
   static RequestError create() => RequestError._();
@@ -81,7 +81,7 @@ class RequestError extends $pb.GeneratedMessage {
   static $pb.PbList<RequestError> createRepeated() => $pb.PbList<RequestError>();
   @$core.pragma('dart2js:noInline')
   static RequestError getDefault() => _defaultInstance ??= $pb.GeneratedMessage.$_defaultFor<RequestError>(create);
-  static RequestError _defaultInstance;
+  static RequestError? _defaultInstance;
 
   @$pb.TagNumber(1)
   $core.int get requestId => $_getIZ(0);
@@ -123,7 +123,7 @@ class Notification extends $pb.GeneratedMessage {
   factory Notification.fromBuffer($core.List<$core.int> i, [$pb.ExtensionRegistry r = $pb.ExtensionRegistry.EMPTY]) => create()..mergeFromBuffer(i, r);
   factory Notification.fromJson($core.String i, [$pb.ExtensionRegistry r = $pb.ExtensionRegistry.EMPTY]) => create()..mergeFromJson(i, r);
   Notification clone() => Notification()..mergeFromMessage(this);
-  Notification copyWith(void Function(Notification) updates) => super.copyWith((message) => updates(message as Notification));
+  Notification copyWith(void Function(Notification) updates) => super.copyWith((message) => updates(message as Notification)) as Notification;
   $pb.BuilderInfo get info_ => _i;
   @$core.pragma('dart2js:noInline')
   static Notification create() => Notification._();
@@ -131,7 +131,7 @@ class Notification extends $pb.GeneratedMessage {
   static $pb.PbList<Notification> createRepeated() => $pb.PbList<Notification>();
   @$core.pragma('dart2js:noInline')
   static Notification getDefault() => _defaultInstance ??= $pb.GeneratedMessage.$_defaultFor<Notification>(create);
-  static Notification _defaultInstance;
+  static Notification? _defaultInstance;
 
   @$pb.TagNumber(1)
   $core.int get subscriptionId => $_getIZ(0);
@@ -165,7 +165,7 @@ class NotificationError extends $pb.GeneratedMessage {
   factory NotificationError.fromBuffer($core.List<$core.int> i, [$pb.ExtensionRegistry r = $pb.ExtensionRegistry.EMPTY]) => create()..mergeFromBuffer(i, r);
   factory NotificationError.fromJson($core.String i, [$pb.ExtensionRegistry r = $pb.ExtensionRegistry.EMPTY]) => create()..mergeFromJson(i, r);
   NotificationError clone() => NotificationError()..mergeFromMessage(this);
-  NotificationError copyWith(void Function(NotificationError) updates) => super.copyWith((message) => updates(message as NotificationError));
+  NotificationError copyWith(void Function(NotificationError) updates) => super.copyWith((message) => updates(message as NotificationError)) as NotificationError;
   $pb.BuilderInfo get info_ => _i;
   @$core.pragma('dart2js:noInline')
   static NotificationError create() => NotificationError._();
@@ -173,7 +173,7 @@ class NotificationError extends $pb.GeneratedMessage {
   static $pb.PbList<NotificationError> createRepeated() => $pb.PbList<NotificationError>();
   @$core.pragma('dart2js:noInline')
   static NotificationError getDefault() => _defaultInstance ??= $pb.GeneratedMessage.$_defaultFor<NotificationError>(create);
-  static NotificationError _defaultInstance;
+  static NotificationError? _defaultInstance;
 
   @$pb.TagNumber(1)
   $core.int get subscriptionId => $_getIZ(0);
diff --git a/lib/gen/protos/mdsflutter.pbenum.dart b/lib/gen/protos/mdsflutter.pbenum.dart
index 4447420..f00db36 100644
--- a/lib/gen/protos/mdsflutter.pbenum.dart
+++ b/lib/gen/protos/mdsflutter.pbenum.dart
@@ -2,6 +2,6 @@
 //  Generated code. Do not modify.
 //  source: protos/mdsflutter.proto
 //
-// @dart = 2.3
+
 // ignore_for_file: annotate_overrides,camel_case_types,unnecessary_const,non_constant_identifier_names,library_prefixes,unused_import,unused_shown_name,return_of_invalid_type
 
diff --git a/lib/gen/protos/mdsflutter.pbjson.dart b/lib/gen/protos/mdsflutter.pbjson.dart
index 8bdb05a..62ae6dd 100644
--- a/lib/gen/protos/mdsflutter.pbjson.dart
+++ b/lib/gen/protos/mdsflutter.pbjson.dart
@@ -2,7 +2,7 @@
 //  Generated code. Do not modify.
 //  source: protos/mdsflutter.proto
 //
-// @dart = 2.3
+
 // ignore_for_file: annotate_overrides,camel_case_types,unnecessary_const,non_constant_identifier_names,library_prefixes,unused_import,unused_shown_name,return_of_invalid_type
 
 const RequestResult$json = const {
diff --git a/lib/gen/protos/mdsflutter.pbserver.dart b/lib/gen/protos/mdsflutter.pbserver.dart
index 47aa4da..73469b4 100644
--- a/lib/gen/protos/mdsflutter.pbserver.dart
+++ b/lib/gen/protos/mdsflutter.pbserver.dart
@@ -2,7 +2,7 @@
 //  Generated code. Do not modify.
 //  source: protos/mdsflutter.proto
 //
-// @dart = 2.3
+
 // ignore_for_file: annotate_overrides,camel_case_types,unnecessary_const,non_constant_identifier_names,library_prefixes,unused_import,unused_shown_name,return_of_invalid_type
 
 export 'mdsflutter.pb.dart';
diff --git a/lib/internal/MdsImpl.dart b/lib/internal/MdsImpl.dart
index e4a1fb0..dce3c1a 100644
--- a/lib/internal/MdsImpl.dart
+++ b/lib/internal/MdsImpl.dart
@@ -1,4 +1,3 @@
-
 import 'dart:async';
 import 'dart:convert';
 import 'dart:typed_data';
@@ -19,10 +18,10 @@ class MdsImpl {
   Map _requestErrorCbMap = Map<int, void Function(String, int)>();
   Map _notifyCbMap = Map<int, void Function(String)>();
   Map _subscriptionErrorCbMap = Map<int, void Function(String, int)>();
-  Map _serialToAddressMap = Map<String, String>();
-  void Function(String, String) _newScannedDeviceCb;
+  Map _serialToAddressMap = Map<String?, String?>();
+  void Function(String?, String?)? _newScannedDeviceCb;
 
-  void startScan(void Function(String, String) onNewDeviceFound) {
+  void startScan(void Function(String?, String?) onNewDeviceFound) {
     _newScannedDeviceCb = onNewDeviceFound;
     _channel.invokeMethod('startScan', null);
   }
@@ -32,11 +31,8 @@ class MdsImpl {
     _channel.invokeMethod('stopScan', null);
   }
 
-  void connect(
-      String address,
-      void Function(String) onConnected,
-      void Function() onDisconnected,
-      void Function() onConnectionError) {
+  void connect(String address, void Function(String) onConnected,
+      void Function() onDisconnected, void Function() onConnectionError) {
     _channel.invokeMethod('connect', {"address": address});
     _connectCbMap[address] = onConnected;
     _disconnectCbMap[address] = onDisconnected;
@@ -47,60 +43,48 @@ class MdsImpl {
     _channel.invokeMethod('disconnect', {"address": address});
   }
 
-  void get(
-      String uri,
-      String contract,
-      void Function(String, int) onSuccess,
+  void get(String uri, String contract, void Function(String, int) onSuccess,
       void Function(String, int) onError) {
     _idCounter++;
     _requestResultCbMap[_idCounter] = onSuccess;
     _requestErrorCbMap[_idCounter] = onError;
-    _channel.invokeMethod('get', <String, dynamic> {
+    _channel.invokeMethod('get', <String, dynamic>{
       "uri": uri,
       "contract": contract,
       "requestId": _idCounter
     });
   }
 
-  void put(
-      String uri,
-      String contract,
-      void Function(String, int) onSuccess,
+  void put(String uri, String contract, void Function(String, int) onSuccess,
       void Function(String, int) onError) {
     _idCounter++;
     _requestResultCbMap[_idCounter] = onSuccess;
     _requestErrorCbMap[_idCounter] = onError;
-    _channel.invokeMethod('put', <String, dynamic> {
+    _channel.invokeMethod('put', <String, dynamic>{
       "uri": uri,
       "contract": contract,
       "requestId": _idCounter
     });
   }
 
-  void post(
-      String uri,
-      String contract,
-      void Function(String, int) onSuccess,
+  void post(String uri, String contract, void Function(String, int) onSuccess,
       void Function(String, int) onError) {
     _idCounter++;
     _requestResultCbMap[_idCounter] = onSuccess;
     _requestErrorCbMap[_idCounter] = onError;
-    _channel.invokeMethod('post', <String, dynamic> {
+    _channel.invokeMethod('post', <String, dynamic>{
       "uri": uri,
       "contract": contract,
       "requestId": _idCounter
     });
   }
 
-  void del(
-      String uri,
-      String contract,
-      void Function(String, int) onSuccess,
+  void del(String uri, String contract, void Function(String, int) onSuccess,
       void Function(String, int) onError) {
     _idCounter++;
     _requestResultCbMap[_idCounter] = onSuccess;
     _requestErrorCbMap[_idCounter] = onError;
-    _channel.invokeMethod('del', <String, dynamic> {
+    _channel.invokeMethod('del', <String, dynamic>{
       "uri": uri,
       "contract": contract,
       "requestId": _idCounter
@@ -131,7 +115,7 @@ class MdsImpl {
       mdsContract = json.encode(contractMap);
     }
 
-    _channel.invokeMethod('subscribe', <String, dynamic> {
+    _channel.invokeMethod('subscribe', <String, dynamic>{
       "uri": mdsUri,
       "contract": mdsContract,
       "requestId": _idCounter,
@@ -163,38 +147,31 @@ class MdsImpl {
   }
 
   void _doConnectSubscription() {
-    subscribe(
-        "MDS/ConnectedDevices",
-        "{}",
-            (d, c) => {},
-            (e, c) => {},
-            (data) {
-          final decoded = jsonDecode(data);
-          final method = decoded["Method"];
-          if (method == "POST") {
-            if (decoded.containsKey("Body")) {
-              final body = decoded["Body"];
-              final deviceInfo = body["DeviceInfo"];
-              final connection = body["Connection"];
-              final uuid = connection["UUID"] as String;
-              final serial = deviceInfo["serial"] as String;
-              _serialToAddressMap[serial] = uuid;
-              _onConnect(uuid, serial);
-            }
-          } else if (method == "DEL") {
-            final body = decoded["Body"];
-            final serial = body["Serial"] as String;
-            if (_serialToAddressMap.containsKey(serial)) {
-              _onDisconnect(_serialToAddressMap[serial]);
-            }
-          }
-        },
-            (e, c) => {}
-    );
+    subscribe("MDS/ConnectedDevices", "{}", (d, c) => {}, (e, c) => {}, (data) {
+      final decoded = jsonDecode(data);
+      final method = decoded["Method"];
+      if (method == "POST") {
+        if (decoded.containsKey("Body")) {
+          final body = decoded["Body"];
+          final deviceInfo = body["DeviceInfo"];
+          final connection = body["Connection"];
+          final uuid = connection["UUID"] as String?;
+          final serial = deviceInfo["serial"] as String?;
+          _serialToAddressMap[serial] = uuid;
+          _onConnect(uuid, serial);
+        }
+      } else if (method == "DEL") {
+        final body = decoded["Body"];
+        final serial = body["Serial"] as String?;
+        if (_serialToAddressMap.containsKey(serial)) {
+          _onDisconnect(_serialToAddressMap[serial]);
+        }
+      }
+    }, (e, c) => {});
   }
 
   Future<void> _onNativeMethodCall(MethodCall call) async {
-    switch(call.method) {
+    switch (call.method) {
       case "onNewScannedDevice":
         Map args = call.arguments;
         _onNewScannedDevice(args["name"], args["address"]);
@@ -203,24 +180,26 @@ class MdsImpl {
         Map args = call.arguments;
         _onConnect(args["address"], args["serial"]);
         break;
-        break;
+
       case "onDisconnect":
-        String address = call.arguments;
+        String? address = call.arguments;
         _onDisconnect(address);
         break;
       case "onConnectionError":
-        String address = call.arguments;
+        String? address = call.arguments;
         _onConnectionError(address);
         break;
       case "onRequestResult":
         final Uint8List proto = call.arguments;
         final RequestResult requestResult = RequestResult.fromBuffer(proto);
-        _onRequestResult(requestResult.requestId, requestResult.data, requestResult.statusCode);
+        _onRequestResult(requestResult.requestId, requestResult.data,
+            requestResult.statusCode);
         break;
       case "onRequestError":
         final Uint8List proto = call.arguments;
         final RequestError requestError = RequestError.fromBuffer(proto);
-        _onRequestError(requestError.requestId, requestError.error, requestError.statusCode);
+        _onRequestError(requestError.requestId, requestError.error,
+            requestError.statusCode);
         break;
       case "onNotification":
         final Uint8List proto = call.arguments;
@@ -230,28 +209,29 @@ class MdsImpl {
       case "onNotificationError":
         final Uint8List proto = call.arguments;
         final NotificationError error = NotificationError.fromBuffer(proto);
-        _onSubscriptionError(error.subscriptionId, error.error, error.statusCode);
+        _onSubscriptionError(
+            error.subscriptionId, error.error, error.statusCode);
         break;
     }
   }
 
-  void _onNewScannedDevice(String name, String address) {
+  void _onNewScannedDevice(String? name, String? address) {
     if (_newScannedDeviceCb != null) {
-      _newScannedDeviceCb(name, address);
+      _newScannedDeviceCb!(name, address);
     }
   }
 
-  void _onConnect(String address, String serial) {
+  void _onConnect(String? address, String? serial) {
     if (_connectCbMap.containsKey(address)) {
-      developer.log("New connected device with serial: " + serial);
+      developer.log("New connected device with serial: " + serial!);
       void Function(String) cb = _connectCbMap[address];
       cb(serial);
     }
   }
 
-  void _onDisconnect(String address) {
+  void _onDisconnect(String? address) {
     if (_disconnectCbMap.containsKey(address)) {
-      developer.log("Device disconnected, address: " + address);
+      developer.log("Device disconnected, address: " + address!);
       void Function() cb = _disconnectCbMap[address];
       cb();
       _connectCbMap.remove(address);
@@ -260,9 +240,9 @@ class MdsImpl {
     }
   }
 
-  void _onConnectionError(String address) {
+  void _onConnectionError(String? address) {
     if (_connectErrorCbMap.containsKey(address)) {
-      developer.log("Device connection error, address: " + address);
+      developer.log("Device connection error, address: " + address!);
       void Function() cb = _connectErrorCbMap[address];
       cb();
       _connectCbMap.remove(address);
diff --git a/pubspec.yaml b/pubspec.yaml
index 375587b..0bddec0 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,17 +1,16 @@
 name: mdsflutter
 description: Flutter plugin for MDS (Movesense Device Service) that is used for communicating with Movesense devices.
-version: 1.0.0
-author: Tugberk Akdogan
+version: 1.1.0
 homepage: https://github.com/tugberka/mdsflutter
 
 environment:
-  sdk: ">=2.7.0 <3.0.0"
-  flutter: ">=1.10.0"
+  sdk: '>=2.12.0 <3.0.0'
+  flutter: ">=2.0.0"
 
 dependencies:
   flutter:
     sdk: flutter
-  protobuf: any
+  protobuf: ^2.0.0
 
 dev_dependencies:
   flutter_test: