diff --git a/example/.flutter-plugins-dependencies b/example/.flutter-plugins-dependencies
index d3651ab..a9c2fa5 100644
--- a/example/.flutter-plugins-dependencies
+++ b/example/.flutter-plugins-dependencies
@@ -1 +1 @@
-{"info":"This is a generated file; do not edit or check into version control.","plugins":{"ios":[{"name":"flutter_cast_framework","path":"/Users/gianluca.paradiso/mydev/cast-your-instructions/flutter_cast_framework/","dependencies":[]}],"android":[{"name":"flutter_cast_framework","path":"/Users/gianluca.paradiso/mydev/cast-your-instructions/flutter_cast_framework/","dependencies":[]}],"macos":[],"linux":[],"windows":[],"web":[]},"dependencyGraph":[{"name":"flutter_cast_framework","dependencies":[]}],"date_created":"2021-09-26 18:47:45.316939","version":"2.5.1"}
\ No newline at end of file
+{"info":"This is a generated file; do not edit or check into version control.","plugins":{"ios":[{"name":"flutter_cast_framework","path":"/Users/gianluca.paradiso/mydev/cast-your-instructions/flutter_cast_framework/","dependencies":[]}],"android":[{"name":"flutter_cast_framework","path":"/Users/gianluca.paradiso/mydev/cast-your-instructions/flutter_cast_framework/","dependencies":[]}],"macos":[],"linux":[],"windows":[],"web":[]},"dependencyGraph":[{"name":"flutter_cast_framework","dependencies":[]}],"date_created":"2021-10-10 18:22:42.460646","version":"2.5.1"}
\ No newline at end of file
diff --git a/lib/src/cast/CastContext.dart b/lib/src/cast/CastContext.dart
index 212b3b1..8d1abbb 100644
--- a/lib/src/cast/CastContext.dart
+++ b/lib/src/cast/CastContext.dart
@@ -18,12 +18,13 @@ class CastContext {
     state.value = CastState.values[castState];
   }
 
-  SessionManager _sessionManager;
+  SessionManager? _sessionManager;
   SessionManager get sessionManager {
-    if (_sessionManager == null) {
-      _sessionManager = SessionManager(_channel);
+    var result = _sessionManager;
+    if (result == null) {
+      _sessionManager = result = SessionManager(_channel);
     }
-    return _sessionManager;
+    return result;
   }
 }
 
diff --git a/lib/src/cast/SessionManager.dart b/lib/src/cast/SessionManager.dart
index 756219b..140f9e7 100644
--- a/lib/src/cast/SessionManager.dart
+++ b/lib/src/cast/SessionManager.dart
@@ -41,21 +41,20 @@ class SessionManager {
     }
   }
 
-  MessageReceivedCallback onMessageReceived;
+  MessageReceivedCallback? onMessageReceived;
 
   void platformOnMessageReceived(dynamic arguments) {
-    if (onMessageReceived == null) return;
+    var thisOnMessageReceived = onMessageReceived;
+
+    if (thisOnMessageReceived == null) return;
     final namespace = arguments['namespace'];
     final message = arguments['message'];
 
-    onMessageReceived(namespace, message);
+    thisOnMessageReceived(namespace, message);
   }
 
   void sendMessage(String namespace, String message) {
-    final argsMap = {
-      'namespace': namespace,
-      'message': message
-    };
+    final argsMap = {'namespace': namespace, 'message': message};
     _channel.invokeMethod(PlatformMethodNames.sendMessage, argsMap);
   }
 }
diff --git a/lib/src/cast/widgets/CastButton.dart b/lib/src/cast/widgets/CastButton.dart
index 07ea17e..3228b32 100644
--- a/lib/src/cast/widgets/CastButton.dart
+++ b/lib/src/cast/widgets/CastButton.dart
@@ -7,7 +7,7 @@ class CastButton extends StatelessWidget {
   final Color color;
 
   CastButton({
-    this.color,
+    required this.color,
   });
 
   @override
diff --git a/lib/src/cast/widgets/CastIcon.dart b/lib/src/cast/widgets/CastIcon.dart
index 968c8c1..7cd9378 100644
--- a/lib/src/cast/widgets/CastIcon.dart
+++ b/lib/src/cast/widgets/CastIcon.dart
@@ -74,9 +74,7 @@ class _CastIconState extends State<CastIcon> with TickerProviderStateMixin {
 class _ConnectingIcon extends StatefulWidget {
   final Color color;
 
-  _ConnectingIcon({
-    this.color = _defaultIconColor,
-  });
+  _ConnectingIcon({required this.color});
 
   @override
   _ConnectingIconState createState() => _ConnectingIconState();
diff --git a/lib/src/flutter_cast_framework.dart b/lib/src/flutter_cast_framework.dart
index 5cc31e7..9ce0cc2 100644
--- a/lib/src/flutter_cast_framework.dart
+++ b/lib/src/flutter_cast_framework.dart
@@ -52,16 +52,17 @@ class FlutterCastFramework {
     });
   }
 
-  static CastContext _castContext;
+  static CastContext? _castContext;
 
   // This must be the plugin entry point
   static CastContext get castContext {
-    if (!_isInitiated || _castContext == null) {
-      _castContext = CastContext(_channel);
+    var castContext = _castContext;
+    if (!_isInitiated || castContext == null) {
+      _castContext = castContext = CastContext(_channel);
       // TODO: find a better way to init the plugin
       _isInitiated = true;
       _init();
     }
-    return _castContext;
+    return castContext;
   }
 }
diff --git a/pubspec.yaml b/pubspec.yaml
index d9f15bc..7d8c0f2 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -4,7 +4,7 @@ version: 0.0.1
 homepage:
 
 environment:
-  sdk: ">=2.1.0 <3.0.0"
+  sdk: ">=2.12.0 <3.0.0"
 
 dependencies:
   flutter: