diff --git a/CHANGELOG.md b/CHANGELOG.md
index 323832a9..25e98b6e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -22,7 +22,7 @@
 * Migrated jael to 4.0.0 (20/20 tests passed)
 * Migrated jael_preprocessor to 3.0.0 (5/5 tests passed)
 * Migrated angel_jael to 4.0.0 (1/1 test passed)
-* Updated pub_sub to 3.0.0 (in progress)
+* Updated pub_sub to 4.0.0 (16/16 tests passed)
 * Updated production to 2.0.0 (in progress)
 * Updated hot to 3.0.0 (in progress)
 * Updated static to 3.0.0 (in progress)
@@ -47,7 +47,7 @@
 * Updated jael_preprocessor to 3.0.0 (5/5 tests passed)
 * Updated test to 3.0.0 (1/1 tests passed)
 * Updated angel_jael to 3.0.0 (1/1 tests passed, Issue with 2 dependencies)
-* Added pub_sub and updated to 3.0.0 (8/16 tests passed)
+* Added pub_sub and updated to 3.0.0 (16/16 tests passed)
 * Updated production to 2.0.0 (0/0 tests passed)
 * Updated hot to 3.0.0 (0/0 tests passed)
 * Updated static to 3.0.0 (12/12 tests passed)
diff --git a/packages/pub_sub/lib/src/isolate/client.dart b/packages/pub_sub/lib/src/isolate/client.dart
index 2776615f..3c8e7d55 100644
--- a/packages/pub_sub/lib/src/isolate/client.dart
+++ b/packages/pub_sub/lib/src/isolate/client.dart
@@ -6,50 +6,49 @@ import '../../pub_sub.dart';
 
 /// A [Client] implementation that communicates via [SendPort]s and [ReceivePort]s.
 class IsolateClient extends Client {
-  final Queue<Completer<String>> _onConnect = new Queue<Completer<String>>();
+  final Queue<Completer<String>> _onConnect = Queue<Completer<String>>();
   final Map<String, Completer<Map>> _requests = {};
   final List<_IsolateClientSubscription> _subscriptions = [];
-  final Uuid _uuid = new Uuid();
+  final Uuid _uuid = Uuid();
 
-  String _id;
+  String? _id;
 
   /// The ID of the client we are authenticating as.
   ///
   /// May be `null`, if and only if we are marked as a trusted source on
   /// the server side.
-  String get clientId => _clientId;
-  String _clientId;
+  String? get clientId => _clientId;
+  String? _clientId;
 
   /// A server's [SendPort] that messages should be sent to.
   final SendPort serverSendPort;
 
   /// A [ReceivePort] that receives messages from the server.
-  final ReceivePort receivePort = new ReceivePort();
+  final ReceivePort receivePort = ReceivePort();
 
-  IsolateClient(String clientId, this.serverSendPort) {
+  IsolateClient(String? clientId, this.serverSendPort) {
     _clientId = clientId;
     receivePort.listen((data) {
       if (data is Map && data['request_id'] is String) {
-        var requestId = data['request_id'] as String;
+        var requestId = data['request_id'] as String?;
         var c = _requests.remove(requestId);
 
         if (c != null && !c.isCompleted) {
           if (data['status'] is! bool) {
             c.completeError(
-                new FormatException('The server sent an invalid response.'));
+                FormatException('The server sent an invalid response.'));
           } else if (!(data['status'] as bool)) {
-            c.completeError(new PubSubException(data['error_message']
-                    ?.toString() ??
+            c.completeError(PubSubException(data['error_message']?.toString() ??
                 'The server sent a failure response, but did not provide an error message.'));
           } else if (data['result'] is! Map) {
-            c.completeError(new FormatException(
+            c.completeError(FormatException(
                 'The server sent a success response, but did not include a result.'));
           } else {
-            c.complete(data['result'] as Map);
+            c.complete(data['result'] as Map?);
           }
         }
       } else if (data is Map && data['id'] is String && _id == null) {
-        _id = data['id'] as String;
+        _id = data['id'] as String?;
 
         for (var c in _onConnect) {
           if (!c.isCompleted) c.complete(_id);
@@ -57,7 +56,8 @@ class IsolateClient extends Client {
 
         _onConnect.clear();
       } else if (data is List && data.length == 2 && data[0] is String) {
-        var eventName = data[0] as String, event = data[1];
+        var eventName = data[0] as String;
+        var event = data[1];
         for (var s in _subscriptions.where((s) => s.eventName == eventName)) {
           if (!s._stream.isClosed) s._stream.add(event);
         }
@@ -66,11 +66,11 @@ class IsolateClient extends Client {
     serverSendPort.send(receivePort.sendPort);
   }
 
-  Future<T> _whenConnected<T>(FutureOr<T> callback()) {
-    if (_id != null)
-      return new Future<T>.sync(callback);
-    else {
-      var c = new Completer<String>();
+  Future<T> _whenConnected<T>(FutureOr<T> Function() callback) {
+    if (_id != null) {
+      return Future<T>.sync(callback);
+    } else {
+      var c = Completer<String>();
       _onConnect.add(c);
       return c.future.then<T>((_) => callback());
     }
@@ -79,7 +79,7 @@ class IsolateClient extends Client {
   @override
   Future publish(String eventName, value) {
     return _whenConnected(() {
-      var c = new Completer<Map>();
+      var c = Completer<Map>();
       var requestId = _uuid.v4();
       _requests[requestId] = c;
       serverSendPort.send({
@@ -93,7 +93,7 @@ class IsolateClient extends Client {
         }
       });
       return c.future.then((result) {
-        _clientId = result['client_id'] as String;
+        _clientId = result['client_id'] as String?;
       });
     });
   }
@@ -101,7 +101,7 @@ class IsolateClient extends Client {
   @override
   Future<ClientSubscription> subscribe(String eventName) {
     return _whenConnected<ClientSubscription>(() {
-      var c = new Completer<Map>();
+      var c = Completer<Map>();
       var requestId = _uuid.v4();
       _requests[requestId] = c;
       serverSendPort.send({
@@ -111,9 +111,9 @@ class IsolateClient extends Client {
         'params': {'client_id': clientId, 'event_name': eventName}
       });
       return c.future.then<ClientSubscription>((result) {
-        _clientId = result['client_id'] as String;
-        var s = new _IsolateClientSubscription(
-            eventName, result['subscription_id'] as String, this);
+        _clientId = result['client_id'] as String?;
+        var s = _IsolateClientSubscription(
+            eventName, result['subscription_id'] as String?, this);
         _subscriptions.add(s);
         return s;
       });
@@ -126,28 +126,30 @@ class IsolateClient extends Client {
 
     for (var c in _onConnect) {
       if (!c.isCompleted) {
-        c.completeError(new StateError(
+        c.completeError(StateError(
             'The client was closed before the server ever accepted the connection.'));
       }
     }
 
     for (var c in _requests.values) {
       if (!c.isCompleted) {
-        c.completeError(new StateError(
+        c.completeError(StateError(
             'The client was closed before the server responded to this request.'));
       }
     }
 
-    for (var s in _subscriptions) s._close();
+    for (var s in _subscriptions) {
+      s._close();
+    }
 
     _requests.clear();
-    return new Future.value();
+    return Future.value();
   }
 }
 
 class _IsolateClientSubscription extends ClientSubscription {
-  final StreamController _stream = new StreamController();
-  final String eventName, id;
+  final StreamController _stream = StreamController();
+  final String? eventName, id;
   final IsolateClient client;
 
   _IsolateClientSubscription(this.eventName, this.id, this.client);
@@ -157,8 +159,8 @@ class _IsolateClientSubscription extends ClientSubscription {
   }
 
   @override
-  StreamSubscription listen(void onData(event),
-      {Function onError, void onDone(), bool cancelOnError}) {
+  StreamSubscription listen(void onData(event)?,
+      {Function? onError, void Function()? onDone, bool? cancelOnError}) {
     return _stream.stream.listen(onData,
         onError: onError, onDone: onDone, cancelOnError: cancelOnError);
   }
@@ -166,7 +168,7 @@ class _IsolateClientSubscription extends ClientSubscription {
   @override
   Future unsubscribe() {
     return client._whenConnected(() {
-      var c = new Completer<Map>();
+      var c = Completer<Map>();
       var requestId = client._uuid.v4();
       client._requests[requestId] = c;
       client.serverSendPort.send({
diff --git a/packages/pub_sub/lib/src/isolate/server.dart b/packages/pub_sub/lib/src/isolate/server.dart
index c442d461..6d75b9f1 100644
--- a/packages/pub_sub/lib/src/isolate/server.dart
+++ b/packages/pub_sub/lib/src/isolate/server.dart
@@ -7,15 +7,15 @@ import '../../pub_sub.dart';
 class IsolateAdapter extends Adapter {
   final Map<String, SendPort> _clients = {};
   final StreamController<PublishRequest> _onPublish =
-      new StreamController<PublishRequest>();
+      StreamController<PublishRequest>();
   final StreamController<SubscriptionRequest> _onSubscribe =
-      new StreamController<SubscriptionRequest>();
+      StreamController<SubscriptionRequest>();
   final StreamController<UnsubscriptionRequest> _onUnsubscribe =
-      new StreamController<UnsubscriptionRequest>();
-  final Uuid _uuid = new Uuid();
+      StreamController<UnsubscriptionRequest>();
+  final Uuid _uuid = Uuid();
 
   /// A [ReceivePort] on which to listen for incoming data.
-  final ReceivePort receivePort = new ReceivePort();
+  final ReceivePort receivePort = ReceivePort();
 
   @override
   Stream<PublishRequest> get onPublish => _onPublish.stream;
@@ -33,7 +33,7 @@ class IsolateAdapter extends Adapter {
     _onPublish.close();
     _onSubscribe.close();
     _onUnsubscribe.close();
-    return new Future.value();
+    return Future.value();
   }
 
   @override
@@ -48,22 +48,22 @@ class IsolateAdapter extends Adapter {
           data['request_id'] is String &&
           data['method'] is String &&
           data['params'] is Map) {
-        var id = data['id'] as String,
-            requestId = data['request_id'] as String,
-            method = data['method'] as String;
-        var params = data['params'] as Map;
-        var sp = _clients[id];
+        var id = data['id'] as String?,
+            requestId = data['request_id'] as String?,
+            method = data['method'] as String?;
+        var params = data['params'] as Map?;
+        var sp = _clients[id!];
 
         if (sp == null) {
           // There's nobody to respond to, so don't send anything to anyone. Oops.
         } else if (method == 'publish') {
-          if (_isValidClientId(params['client_id']) &&
+          if (_isValidClientId(params!['client_id']) &&
               params['event_name'] is String &&
               params.containsKey('value')) {
-            var clientId = params['client_id'] as String,
-                eventName = params['event_name'] as String;
+            var clientId = params['client_id'] as String?,
+                eventName = params['event_name'] as String?;
             var value = params['value'];
-            var rq = new _IsolatePublishRequestImpl(
+            var rq = _IsolatePublishRequestImpl(
                 requestId, clientId, eventName, value, sp);
             _onPublish.add(rq);
           } else {
@@ -74,11 +74,11 @@ class IsolateAdapter extends Adapter {
             });
           }
         } else if (method == 'subscribe') {
-          if (_isValidClientId(params['client_id']) &&
+          if (_isValidClientId(params!['client_id']) &&
               params['event_name'] is String) {
-            var clientId = params['client_id'] as String,
-                eventName = params['event_name'] as String;
-            var rq = new _IsolateSubscriptionRequestImpl(
+            var clientId = params['client_id'] as String?,
+                eventName = params['event_name'] as String?;
+            var rq = _IsolateSubscriptionRequestImpl(
                 clientId, eventName, sp, requestId, _uuid);
             _onSubscribe.add(rq);
           } else {
@@ -89,11 +89,11 @@ class IsolateAdapter extends Adapter {
             });
           }
         } else if (method == 'unsubscribe') {
-          if (_isValidClientId(params['client_id']) &&
+          if (_isValidClientId(params!['client_id']) &&
               params['subscription_id'] is String) {
-            var clientId = params['client_id'] as String,
-                subscriptionId = params['subscription_id'] as String;
-            var rq = new _IsolateUnsubscriptionRequestImpl(
+            var clientId = params['client_id'] as String?,
+                subscriptionId = params['subscription_id'] as String?;
+            var rq = _IsolateUnsubscriptionRequestImpl(
                 clientId, subscriptionId, sp, requestId);
             _onUnsubscribe.add(rq);
           } else {
@@ -132,17 +132,17 @@ class IsolateAdapter extends Adapter {
 
 class _IsolatePublishRequestImpl extends PublishRequest {
   @override
-  final String clientId;
+  final String? clientId;
 
   @override
-  final String eventName;
+  final String? eventName;
 
   @override
   final value;
 
   final SendPort sendPort;
 
-  final String requestId;
+  final String? requestId;
 
   _IsolatePublishRequestImpl(
       this.requestId, this.clientId, this.eventName, this.value, this.sendPort);
@@ -171,14 +171,14 @@ class _IsolatePublishRequestImpl extends PublishRequest {
 
 class _IsolateSubscriptionRequestImpl extends SubscriptionRequest {
   @override
-  final String clientId;
+  final String? clientId;
 
   @override
-  final String eventName;
+  final String? eventName;
 
   final SendPort sendPort;
 
-  final String requestId;
+  final String? requestId;
 
   final Uuid _uuid;
 
@@ -195,22 +195,22 @@ class _IsolateSubscriptionRequestImpl extends SubscriptionRequest {
   }
 
   @override
-  FutureOr<Subscription> accept(String clientId) {
+  FutureOr<Subscription> accept(String? clientId) {
     var id = _uuid.v4();
     sendPort.send({
       'status': true,
       'request_id': requestId,
       'result': {'subscription_id': id, 'client_id': clientId}
     });
-    return new _IsolateSubscriptionImpl(clientId, id, eventName, sendPort);
+    return _IsolateSubscriptionImpl(clientId, id, eventName, sendPort);
   }
 }
 
 class _IsolateSubscriptionImpl extends Subscription {
   @override
-  final String clientId, id;
+  final String? clientId, id;
 
-  final String eventName;
+  final String? eventName;
 
   final SendPort sendPort;
 
@@ -225,14 +225,14 @@ class _IsolateSubscriptionImpl extends Subscription {
 
 class _IsolateUnsubscriptionRequestImpl extends UnsubscriptionRequest {
   @override
-  final String clientId;
+  final String? clientId;
 
   @override
-  final String subscriptionId;
+  final String? subscriptionId;
 
   final SendPort sendPort;
 
-  final String requestId;
+  final String? requestId;
 
   _IsolateUnsubscriptionRequestImpl(
       this.clientId, this.subscriptionId, this.sendPort, this.requestId);
diff --git a/packages/pub_sub/lib/src/json_rpc/client.dart b/packages/pub_sub/lib/src/json_rpc/client.dart
index e72cbedc..e9146e04 100644
--- a/packages/pub_sub/lib/src/json_rpc/client.dart
+++ b/packages/pub_sub/lib/src/json_rpc/client.dart
@@ -8,43 +8,42 @@ import '../../pub_sub.dart';
 class JsonRpc2Client extends Client {
   final Map<String, Completer<Map>> _requests = {};
   final List<_JsonRpc2ClientSubscription> _subscriptions = [];
-  final Uuid _uuid = new Uuid();
+  final Uuid _uuid = Uuid();
 
-  json_rpc_2.Peer _peer;
+  json_rpc_2.Peer? _peer;
 
   /// The ID of the client we are authenticating as.
   ///
   /// May be `null`, if and only if we are marked as a trusted source on
   /// the server side.
-  String get clientId => _clientId;
-  String _clientId;
+  String? get clientId => _clientId;
+  String? _clientId;
 
-  JsonRpc2Client(String clientId, StreamChannel<String> channel) {
+  JsonRpc2Client(String? clientId, StreamChannel<String> channel) {
     _clientId = clientId;
-    _peer = new json_rpc_2.Peer(channel);
+    _peer = json_rpc_2.Peer(channel);
 
-    _peer.registerMethod('event', (json_rpc_2.Parameters params) {
-      var eventName = params['event_name'].asString,
-          event = params['value'].value;
+    _peer!.registerMethod('event', (json_rpc_2.Parameters params) {
+      String? eventName = params['event_name'].asString;
+      var event = params['value'].value;
       for (var s in _subscriptions.where((s) => s.eventName == eventName)) {
         if (!s._stream.isClosed) s._stream.add(event);
       }
     });
 
-    _peer.registerFallback((json_rpc_2.Parameters params) {
+    _peer!.registerFallback((json_rpc_2.Parameters params) {
       var c = _requests.remove(params.method);
 
-      if (c == null)
-        throw new json_rpc_2.RpcException.methodNotFound(params.method);
-      else {
+      if (c == null) {
+        throw json_rpc_2.RpcException.methodNotFound(params.method);
+      } else {
         var data = params.asMap;
 
         if (data['status'] is! bool) {
           c.completeError(
-              new FormatException('The server sent an invalid response.'));
+              FormatException('The server sent an invalid response.'));
         } else if (!(data['status'] as bool)) {
-          c.completeError(new PubSubException(data['error_message']
-                  ?.toString() ??
+          c.completeError(PubSubException(data['error_message']?.toString() ??
               'The server sent a failure response, but did not provide an error message.'));
         } else {
           c.complete(data);
@@ -52,39 +51,39 @@ class JsonRpc2Client extends Client {
       }
     });
 
-    _peer.listen();
+    _peer!.listen();
   }
 
   @override
   Future publish(String eventName, value) {
-    var c = new Completer<Map>();
+    var c = Completer<Map>();
     var requestId = _uuid.v4();
     _requests[requestId] = c;
-    _peer.sendNotification('publish', {
+    _peer!.sendNotification('publish', {
       'request_id': requestId,
       'client_id': clientId,
       'event_name': eventName,
       'value': value
     });
     return c.future.then((data) {
-      _clientId = data['result']['client_id'] as String;
+      _clientId = data['result']['client_id'] as String?;
     });
   }
 
   @override
   Future<ClientSubscription> subscribe(String eventName) {
-    var c = new Completer<Map>();
+    var c = Completer<Map>();
     var requestId = _uuid.v4();
     _requests[requestId] = c;
-    _peer.sendNotification('subscribe', {
+    _peer!.sendNotification('subscribe', {
       'request_id': requestId,
       'client_id': clientId,
       'event_name': eventName
     });
     return c.future.then<ClientSubscription>((result) {
-      _clientId = result['client_id'] as String;
-      var s = new _JsonRpc2ClientSubscription(
-          eventName, result['subscription_id'] as String, this);
+      _clientId = result['client_id'] as String?;
+      var s = _JsonRpc2ClientSubscription(
+          eventName, result['subscription_id'] as String?, this);
       _subscriptions.add(s);
       return s;
     });
@@ -92,11 +91,11 @@ class JsonRpc2Client extends Client {
 
   @override
   Future close() {
-    if (_peer?.isClosed != true) _peer.close();
+    if (_peer?.isClosed != true) _peer!.close();
 
     for (var c in _requests.values) {
       if (!c.isCompleted) {
-        c.completeError(new StateError(
+        c.completeError(StateError(
             'The client was closed before the server responded to this request.'));
       }
     }
@@ -104,13 +103,13 @@ class JsonRpc2Client extends Client {
     for (var s in _subscriptions) s._close();
 
     _requests.clear();
-    return new Future.value();
+    return Future.value();
   }
 }
 
 class _JsonRpc2ClientSubscription extends ClientSubscription {
-  final StreamController _stream = new StreamController();
-  final String eventName, id;
+  final StreamController _stream = StreamController();
+  final String? eventName, id;
   final JsonRpc2Client client;
 
   _JsonRpc2ClientSubscription(this.eventName, this.id, this.client);
@@ -120,18 +119,18 @@ class _JsonRpc2ClientSubscription extends ClientSubscription {
   }
 
   @override
-  StreamSubscription listen(void onData(event),
-      {Function onError, void onDone(), bool cancelOnError}) {
+  StreamSubscription listen(void onData(event)?,
+      {Function? onError, void Function()? onDone, bool? cancelOnError}) {
     return _stream.stream.listen(onData,
         onError: onError, onDone: onDone, cancelOnError: cancelOnError);
   }
 
   @override
   Future unsubscribe() {
-    var c = new Completer<Map>();
+    var c = Completer<Map>();
     var requestId = client._uuid.v4();
     client._requests[requestId] = c;
-    client._peer.sendNotification('unsubscribe', {
+    client._peer!.sendNotification('unsubscribe', {
       'request_id': requestId,
       'client_id': client.clientId,
       'subscription_id': id
diff --git a/packages/pub_sub/lib/src/json_rpc/server.dart b/packages/pub_sub/lib/src/json_rpc/server.dart
index 5cf4fb84..e7080ce1 100644
--- a/packages/pub_sub/lib/src/json_rpc/server.dart
+++ b/packages/pub_sub/lib/src/json_rpc/server.dart
@@ -7,16 +7,16 @@ import '../../pub_sub.dart';
 /// A [Adapter] implementation that communicates via JSON RPC 2.0.
 class JsonRpc2Adapter extends Adapter {
   final StreamController<PublishRequest> _onPublish =
-      new StreamController<PublishRequest>();
+      StreamController<PublishRequest>();
   final StreamController<SubscriptionRequest> _onSubscribe =
-      new StreamController<SubscriptionRequest>();
+      StreamController<SubscriptionRequest>();
   final StreamController<UnsubscriptionRequest> _onUnsubscribe =
-      new StreamController<UnsubscriptionRequest>();
+      StreamController<UnsubscriptionRequest>();
 
   final List<json_rpc_2.Peer> _peers = [];
-  final Uuid _uuid = new Uuid();
+  final Uuid _uuid = Uuid();
 
-  json_rpc_2.Peer _peer;
+  json_rpc_2.Peer? _peer;
 
   /// A [Stream] of incoming clients, who can both send and receive string data.
   final Stream<StreamChannel<String>> clientStream;
@@ -44,10 +44,10 @@ class JsonRpc2Adapter extends Adapter {
 
     Future.wait(_peers.where((s) => !s.isClosed).map((s) => s.close()))
         .then((_) => _peers.clear());
-    return new Future.value();
+    return Future.value();
   }
 
-  String _getClientId(json_rpc_2.Parameters params) {
+  String? _getClientId(json_rpc_2.Parameters params) {
     try {
       return params['client_id'].asString;
     } catch (_) {
@@ -58,14 +58,14 @@ class JsonRpc2Adapter extends Adapter {
   @override
   void start() {
     clientStream.listen((client) {
-      var peer = _peer = new json_rpc_2.Peer(client);
+      var peer = _peer = json_rpc_2.Peer(client);
 
       peer.registerMethod('publish', (json_rpc_2.Parameters params) async {
         var requestId = params['request_id'].asString;
         var clientId = _getClientId(params);
         var eventName = params['event_name'].asString;
         var value = params['value'].value;
-        var rq = new _JsonRpc2PublishRequestImpl(
+        var rq = _JsonRpc2PublishRequestImpl(
             requestId, clientId, eventName, value, peer);
         _onPublish.add(rq);
       });
@@ -74,7 +74,7 @@ class JsonRpc2Adapter extends Adapter {
         var requestId = params['request_id'].asString;
         var clientId = _getClientId(params);
         var eventName = params['event_name'].asString;
-        var rq = new _JsonRpc2SubscriptionRequestImpl(
+        var rq = _JsonRpc2SubscriptionRequestImpl(
             clientId, eventName, requestId, peer, _uuid);
         _onSubscribe.add(rq);
       });
@@ -83,7 +83,7 @@ class JsonRpc2Adapter extends Adapter {
         var requestId = params['request_id'].asString;
         var clientId = _getClientId(params);
         var subscriptionId = params['subscription_id'].asString;
-        var rq = new _JsonRpc2UnsubscriptionRequestImpl(
+        var rq = _JsonRpc2UnsubscriptionRequestImpl(
             clientId, subscriptionId, peer, requestId);
         _onUnsubscribe.add(rq);
       });
@@ -104,8 +104,14 @@ class JsonRpc2Adapter extends Adapter {
 }
 
 class _JsonRpc2PublishRequestImpl extends PublishRequest {
-  final String requestId, clientId, eventName;
+  final String requestId;
+
+  @override
+  final String? clientId, eventName;
+
+  @override
   final value;
+
   final json_rpc_2.Peer peer;
 
   _JsonRpc2PublishRequestImpl(
@@ -135,7 +141,7 @@ class _JsonRpc2PublishRequestImpl extends PublishRequest {
 
 class _JsonRpc2SubscriptionRequestImpl extends SubscriptionRequest {
   @override
-  final String clientId, eventName;
+  final String? clientId, eventName;
 
   final String requestId;
 
@@ -147,7 +153,7 @@ class _JsonRpc2SubscriptionRequestImpl extends SubscriptionRequest {
       this.clientId, this.eventName, this.requestId, this.peer, this._uuid);
 
   @override
-  FutureOr<Subscription> accept(String clientId) {
+  FutureOr<Subscription> accept(String? clientId) {
     var id = _uuid.v4();
     peer.sendNotification(requestId, {
       'status': true,
@@ -155,7 +161,7 @@ class _JsonRpc2SubscriptionRequestImpl extends SubscriptionRequest {
       'subscription_id': id,
       'client_id': clientId
     });
-    return new _JsonRpc2SubscriptionImpl(clientId, id, eventName, peer);
+    return _JsonRpc2SubscriptionImpl(clientId, id, eventName, peer);
   }
 
   @override
@@ -170,9 +176,9 @@ class _JsonRpc2SubscriptionRequestImpl extends SubscriptionRequest {
 
 class _JsonRpc2SubscriptionImpl extends Subscription {
   @override
-  final String clientId, id;
+  final String? clientId, id;
 
-  final String eventName;
+  final String? eventName;
 
   final json_rpc_2.Peer peer;
 
@@ -186,7 +192,7 @@ class _JsonRpc2SubscriptionImpl extends Subscription {
 
 class _JsonRpc2UnsubscriptionRequestImpl extends UnsubscriptionRequest {
   @override
-  final String clientId;
+  final String? clientId;
 
   @override
   final String subscriptionId;
diff --git a/packages/pub_sub/lib/src/protocol/server/publish.dart b/packages/pub_sub/lib/src/protocol/server/publish.dart
index 03fb7903..b6cbf95b 100644
--- a/packages/pub_sub/lib/src/protocol/server/publish.dart
+++ b/packages/pub_sub/lib/src/protocol/server/publish.dart
@@ -1,10 +1,10 @@
 /// Represents a request to publish information to other clients.
 abstract class PublishRequest {
   /// The ID of the client sending this request.
-  String get clientId;
+  String? get clientId;
 
   /// The name of the event to be sent.
-  String get eventName;
+  String? get eventName;
 
   /// The value to be published as an event.
   dynamic get value;
@@ -22,7 +22,7 @@ class PublishResponse {
   final int listeners;
 
   /// The client ID returned the server. Significant in cases where an ad-hoc client was registered.
-  final String clientId;
+  final String? clientId;
 
   const PublishResponse(this.listeners, this.clientId);
 }
diff --git a/packages/pub_sub/lib/src/protocol/server/server.dart b/packages/pub_sub/lib/src/protocol/server/server.dart
index 0ee8fdb5..b0cc08d7 100644
--- a/packages/pub_sub/lib/src/protocol/server/server.dart
+++ b/packages/pub_sub/lib/src/protocol/server/server.dart
@@ -2,6 +2,7 @@ import 'dart:async';
 import 'dart:math';
 import 'adapter.dart';
 import 'client.dart';
+import 'package:collection/collection.dart' show IterableExtension;
 import 'publish.dart';
 import 'subscription.dart';
 
@@ -12,32 +13,32 @@ import 'subscription.dart';
 class Server {
   final List<Adapter> _adapters = [];
   final List<ClientInfo> _clients = [];
-  final _rnd = new Random.secure();
-  final Map<String, List<Subscription>> _subscriptions = {};
+  final _rnd = Random.secure();
+  final Map<String?, List<Subscription>> _subscriptions = {};
   bool _started = false;
   int _adHocIds = 0;
 
   /// Initialize a server, optionally with a number of [adapters].
   Server([Iterable<Adapter> adapters = const []]) {
-    _adapters.addAll(adapters ?? []);
+    _adapters.addAll(adapters);
   }
 
   /// Adds a new [Adapter] to adapt incoming clients from a new interface.
   void addAdapter(Adapter adapter) {
-    if (_started)
-      throw new StateError(
+    if (_started) {
+      throw StateError(
           'You cannot add new adapters after the server has started listening.');
-    else {
+    } else {
       _adapters.add(adapter);
     }
   }
 
   /// Registers a new client with the server.
   void registerClient(ClientInfo client) {
-    if (_started)
-      throw new StateError(
+    if (_started) {
+      throw StateError(
           'You cannot register new clients after the server has started listening.');
-    else {
+    } else {
       _clients.add(client);
     }
   }
@@ -48,25 +49,26 @@ class Server {
     _adapters.clear();
     _clients.clear();
     _subscriptions.clear();
-    return new Future.value();
+    return Future.value();
   }
 
   String _newClientId() {
     // Create an unpredictable-enough ID. The harder it is for an attacker to guess, the better.
     var id =
-        'pub_sub::adhoc_client${_rnd.nextDouble()}::${_adHocIds++}:${new DateTime.now().millisecondsSinceEpoch * _rnd.nextDouble()}';
+        'pub_sub::adhoc_client${_rnd.nextDouble()}::${_adHocIds++}:${DateTime.now().millisecondsSinceEpoch * _rnd.nextDouble()}';
 
     // This client is coming from a trusted source, and can therefore both publish and subscribe.
-    _clients.add(new ClientInfo(id));
+    _clients.add(ClientInfo(id));
     return id;
   }
 
   void start() {
-    if (_adapters.isEmpty)
-      throw new StateError(
+    if (_adapters.isEmpty) {
+      throw StateError(
           'Cannot start a SyncServer that has no adapters attached.');
-    else if (_started)
-      throw new StateError('A SyncServer may only be started once.');
+    } else if (_started) {
+      throw StateError('A SyncServer may only be started once.');
+    }
 
     _started = true;
 
@@ -77,15 +79,14 @@ class Server {
     for (var adapter in _adapters) {
       // Handle publishes
       adapter.onPublish.listen((rq) {
-        ClientInfo client;
-        String clientId;
+        ClientInfo? client;
+        String? clientId;
 
         if (rq.clientId?.isNotEmpty == true ||
             adapter.isTrustedPublishRequest(rq)) {
           clientId =
               rq.clientId?.isNotEmpty == true ? rq.clientId : _newClientId();
-          client =
-              _clients.firstWhere((c) => c.id == clientId, orElse: () => null);
+          client = _clients.firstWhereOrNull((c) => c.id == clientId);
         }
 
         if (client == null) {
@@ -98,28 +99,27 @@ class Server {
               [];
 
           if (listeners.isEmpty) {
-            rq.accept(new PublishResponse(0, clientId));
+            rq.accept(PublishResponse(0, clientId));
           } else {
             for (var listener in listeners) {
               listener.dispatch(rq.value);
             }
 
-            rq.accept(new PublishResponse(listeners.length, clientId));
+            rq.accept(PublishResponse(listeners.length, clientId));
           }
         }
       });
 
       // Listen for incoming subscriptions
       adapter.onSubscribe.listen((rq) async {
-        ClientInfo client;
-        String clientId;
+        ClientInfo? client;
+        String? clientId;
 
         if (rq.clientId?.isNotEmpty == true ||
             adapter.isTrustedSubscriptionRequest(rq)) {
           clientId =
               rq.clientId?.isNotEmpty == true ? rq.clientId : _newClientId();
-          client =
-              _clients.firstWhere((c) => c.id == clientId, orElse: () => null);
+          client = _clients.firstWhereOrNull((c) => c.id == clientId);
         }
 
         if (client == null) {
@@ -135,12 +135,11 @@ class Server {
 
       // Unregister subscriptions on unsubscribe
       adapter.onUnsubscribe.listen((rq) {
-        Subscription toRemove;
-        List<Subscription> sourceList;
+        Subscription? toRemove;
+        late List<Subscription> sourceList;
 
         for (var list in _subscriptions.values) {
-          toRemove = list.firstWhere((s) => s.id == rq.subscriptionId,
-              orElse: () => null);
+          toRemove = list.firstWhereOrNull((s) => s.id == rq.subscriptionId);
           if (toRemove != null) {
             sourceList = list;
             break;
diff --git a/packages/pub_sub/lib/src/protocol/server/subscription.dart b/packages/pub_sub/lib/src/protocol/server/subscription.dart
index 57efcbf5..9f5db231 100644
--- a/packages/pub_sub/lib/src/protocol/server/subscription.dart
+++ b/packages/pub_sub/lib/src/protocol/server/subscription.dart
@@ -3,15 +3,15 @@ import 'dart:async';
 /// Represents a request to subscribe to an event.
 abstract class SubscriptionRequest {
   /// The ID of the client requesting to subscribe.
-  String get clientId;
+  String? get clientId;
 
   /// The name of the event the client wants to subscribe to.
-  String get eventName;
+  String? get eventName;
 
   /// Accept the request, and grant the client access to subscribe to the event.
   ///
   /// Includes the client's ID, which is necessary for ad-hoc clients.
-  FutureOr<Subscription> accept(String clientId);
+  FutureOr<Subscription> accept(String? clientId);
 
   /// Deny the request with an error message.
   void reject(String errorMessage);
@@ -20,10 +20,10 @@ abstract class SubscriptionRequest {
 /// Represents a request to unsubscribe to an event.
 abstract class UnsubscriptionRequest {
   /// The ID of the client requesting to unsubscribe.
-  String get clientId;
+  String? get clientId;
 
   /// The name of the event the client wants to unsubscribe from.
-  String get subscriptionId;
+  String? get subscriptionId;
 
   /// Accept the request.
   FutureOr<void> accept();
@@ -37,10 +37,10 @@ abstract class UnsubscriptionRequest {
 /// Also provides a means to fire an event.
 abstract class Subscription {
   /// A unique identifier for this subscription.
-  String get id;
+  String? get id;
 
   /// The ID of the client who requested this subscription.
-  String get clientId;
+  String? get clientId;
 
   /// Alerts a client of an event.
   void dispatch(event);
diff --git a/packages/pub_sub/pubspec.yaml b/packages/pub_sub/pubspec.yaml
index f214636a..90fd4058 100644
--- a/packages/pub_sub/pubspec.yaml
+++ b/packages/pub_sub/pubspec.yaml
@@ -5,11 +5,12 @@ author: Tobe O <thosakwe@gmail.com>
 homepage: https://github.com/thosakwe/pub_sub
 publish_to: none
 environment:
-  sdk: ">=2.10.0 <3.0.0"
+  sdk: '>=2.12.0 <3.0.0'
 dependencies:
-  json_rpc_2: ^2.0.0
-  stream_channel: ">=1.0.0 <3.0.0"
-  uuid: ^3.0.1
+  json_rpc_2: ^3.0.0
+  stream_channel: ^2.1.0
+  uuid: ^3.0.4
+  collection: ^1.15.0-nullsafety.4
 dev_dependencies:
-  pedantic: ^1.0.0
-  test: ^1.0.0
+  pedantic: ^1.11.0
+  test: ^1.17.3
diff --git a/packages/pub_sub/test/isolate_test.dart b/packages/pub_sub/test/isolate_test.dart
index 1d1c0136..5a3ac8d8 100644
--- a/packages/pub_sub/test/isolate_test.dart
+++ b/packages/pub_sub/test/isolate_test.dart
@@ -3,23 +3,23 @@ import 'package:pub_sub/pub_sub.dart';
 import 'package:pub_sub/isolate.dart';
 import 'package:test/test.dart';
 
-main() {
-  Server server;
-  Client client1, client2, client3;
-  IsolateClient trustedClient;
-  IsolateAdapter adapter;
+void main() {
+  late Server server;
+  late Client client1, client2, client3;
+  late IsolateClient trustedClient;
+  late IsolateAdapter adapter;
 
   setUp(() async {
-    adapter = new IsolateAdapter();
+    adapter = IsolateAdapter();
     client1 =
-        new IsolateClient('isolate_test::secret', adapter.receivePort.sendPort);
-    client2 = new IsolateClient(
-        'isolate_test::secret2', adapter.receivePort.sendPort);
-    client3 = new IsolateClient(
-        'isolate_test::secret3', adapter.receivePort.sendPort);
-    trustedClient = new IsolateClient(null, adapter.receivePort.sendPort);
+        IsolateClient('isolate_test::secret', adapter.receivePort.sendPort);
+    client2 =
+        IsolateClient('isolate_test::secret2', adapter.receivePort.sendPort);
+    client3 =
+        IsolateClient('isolate_test::secret3', adapter.receivePort.sendPort);
+    trustedClient = IsolateClient(null, adapter.receivePort.sendPort);
 
-    server = new Server([adapter])
+    server = Server([adapter])
       ..registerClient(const ClientInfo('isolate_test::secret'))
       ..registerClient(const ClientInfo('isolate_test::secret2'))
       ..registerClient(const ClientInfo('isolate_test::secret3'))
@@ -51,7 +51,7 @@ main() {
       expect(trustedClient.clientId, isNotNull);
     });
     test('can sub/unsub', () async {
-      String clientId;
+      String? clientId;
       await trustedClient.publish('heyaaa', 'byeaa');
       expect(clientId = trustedClient.clientId, isNotNull);
 
@@ -88,7 +88,7 @@ main() {
   group('isolate_server', () {
     test('reject unknown client id', () async {
       try {
-        var client = new IsolateClient(
+        var client = IsolateClient(
             'isolate_test::invalid', adapter.receivePort.sendPort);
         await client.publish('foo', 'bar');
         throw 'Invalid client ID\'s should throw an error, but they do not.';
@@ -99,7 +99,7 @@ main() {
 
     test('reject unprivileged publish', () async {
       try {
-        var client = new IsolateClient(
+        var client = IsolateClient(
             'isolate_test::no_publish', adapter.receivePort.sendPort);
         await client.publish('foo', 'bar');
         throw 'Unprivileged publishes should throw an error, but they do not.';
@@ -110,7 +110,7 @@ main() {
 
     test('reject unprivileged subscribe', () async {
       try {
-        var client = new IsolateClient(
+        var client = IsolateClient(
             'isolate_test::no_subscribe', adapter.receivePort.sendPort);
         await client.subscribe('foo');
         throw 'Unprivileged subscribes should throw an error, but they do not.';
diff --git a/packages/pub_sub/test/json_rpc_2_test.dart b/packages/pub_sub/test/json_rpc_2_test.dart
index 2e959552..ff02ae3b 100644
--- a/packages/pub_sub/test/json_rpc_2_test.dart
+++ b/packages/pub_sub/test/json_rpc_2_test.dart
@@ -6,17 +6,17 @@ import 'package:pub_sub/json_rpc_2.dart';
 import 'package:stream_channel/stream_channel.dart';
 import 'package:test/test.dart';
 
-main() {
-  ServerSocket serverSocket;
-  Server server;
-  Client client1, client2, client3;
-  JsonRpc2Client trustedClient;
+void main() {
+  late ServerSocket serverSocket;
+  late Server server;
+  late Client client1, client2, client3;
+  late JsonRpc2Client trustedClient;
   JsonRpc2Adapter adapter;
 
   setUp(() async {
     serverSocket = await ServerSocket.bind(InternetAddress.loopbackIPv4, 0);
 
-    adapter = new JsonRpc2Adapter(
+    adapter = JsonRpc2Adapter(
         serverSocket.map<StreamChannel<String>>(streamSocket),
         isTrusted: true);
 
@@ -29,15 +29,12 @@ main() {
     var socket4 =
         await Socket.connect(InternetAddress.loopbackIPv4, serverSocket.port);
 
-    client1 =
-        new JsonRpc2Client('json_rpc_2_test::secret', streamSocket(socket1));
-    client2 =
-        new JsonRpc2Client('json_rpc_2_test::secret2', streamSocket(socket2));
-    client3 =
-        new JsonRpc2Client('json_rpc_2_test::secret3', streamSocket(socket3));
-    trustedClient = new JsonRpc2Client(null, streamSocket(socket4));
+    client1 = JsonRpc2Client('json_rpc_2_test::secret', streamSocket(socket1));
+    client2 = JsonRpc2Client('json_rpc_2_test::secret2', streamSocket(socket2));
+    client3 = JsonRpc2Client('json_rpc_2_test::secret3', streamSocket(socket3));
+    trustedClient = JsonRpc2Client(null, streamSocket(socket4));
 
-    server = new Server([adapter])
+    server = Server([adapter])
       ..registerClient(const ClientInfo('json_rpc_2_test::secret'))
       ..registerClient(const ClientInfo('json_rpc_2_test::secret2'))
       ..registerClient(const ClientInfo('json_rpc_2_test::secret3'))
@@ -64,7 +61,7 @@ main() {
       expect(trustedClient.clientId, isNotNull);
     });
     test('can sub/unsub', () async {
-      String clientId;
+      String? clientId;
       await trustedClient.publish('heyaaa', 'byeaa');
       expect(clientId = trustedClient.clientId, isNotNull);
 
@@ -104,7 +101,7 @@ main() {
         var sock = await Socket.connect(
             InternetAddress.loopbackIPv4, serverSocket.port);
         var client =
-            new JsonRpc2Client('json_rpc_2_test::invalid', streamSocket(sock));
+            JsonRpc2Client('json_rpc_2_test::invalid', streamSocket(sock));
         await client.publish('foo', 'bar');
         throw 'Invalid client ID\'s should throw an error, but they do not.';
       } on PubSubException catch (e) {
@@ -116,8 +113,8 @@ main() {
       try {
         var sock = await Socket.connect(
             InternetAddress.loopbackIPv4, serverSocket.port);
-        var client = new JsonRpc2Client(
-            'json_rpc_2_test::no_publish', streamSocket(sock));
+        var client =
+            JsonRpc2Client('json_rpc_2_test::no_publish', streamSocket(sock));
         await client.publish('foo', 'bar');
         throw 'Unprivileged publishes should throw an error, but they do not.';
       } on PubSubException catch (e) {
@@ -129,8 +126,8 @@ main() {
       try {
         var sock = await Socket.connect(
             InternetAddress.loopbackIPv4, serverSocket.port);
-        var client = new JsonRpc2Client(
-            'json_rpc_2_test::no_subscribe', streamSocket(sock));
+        var client =
+            JsonRpc2Client('json_rpc_2_test::no_subscribe', streamSocket(sock));
         await client.subscribe('foo');
         throw 'Unprivileged subscribes should throw an error, but they do not.';
       } on PubSubException catch (e) {
@@ -141,18 +138,20 @@ main() {
 }
 
 StreamChannel<String> streamSocket(Socket socket) {
-  var channel = new _SocketStreamChannel(socket);
-  return channel.transform(new StreamChannelTransformer.fromCodec(utf8));
+  var channel = _SocketStreamChannel(socket);
+  return channel
+      .cast<List<int>>()
+      .transform(StreamChannelTransformer.fromCodec(utf8));
 }
 
 class _SocketStreamChannel extends StreamChannelMixin<List<int>> {
-  _SocketSink _sink;
+  _SocketSink? _sink;
   final Socket socket;
 
   _SocketStreamChannel(this.socket);
 
   @override
-  StreamSink<List<int>> get sink => _sink ??= new _SocketSink(socket);
+  StreamSink<List<int>> get sink => _sink ??= _SocketSink(socket);
 
   @override
   Stream<List<int>> get stream => socket;
@@ -169,7 +168,7 @@ class _SocketSink extends StreamSink<List<int>> {
   }
 
   @override
-  void addError(Object error, [StackTrace stackTrace]) {
+  void addError(Object error, [StackTrace? stackTrace]) {
     Zone.current.errorCallback(error, stackTrace);
   }