Migrate to null safety

lib/futuristic.dart

@@ -18,47 +18,45 @@ class Futuristic<T> extends StatefulWidget {
 
   /// Widget to display while the [Future] is executing.
   /// If null, a [CircularProgressIndicator] will be displayed.
-  final WidgetBuilder busyBuilder;
+  final WidgetBuilder? busyBuilder;
 
   /// Widget to display when the [Future] has completed with an error.
   /// If null, [initialBuilder] will be displayed again.
   /// The [Object] is the [Error] or [Exception] returned by the [Future].
   /// Call [VoidCallback] to start executing the [Future] again.
-  final Widget Function(BuildContext, Object, VoidCallback) errorBuilder;
+  final Widget Function(BuildContext, Object, VoidCallback)? errorBuilder;
 
   /// Widget to display when the [Future] has completed successfully.
   /// If null, [initialBuilder] will be displayed again.
-  final Widget Function(BuildContext, T) dataBuilder;
+  final Widget Function(BuildContext, T)? dataBuilder;
 
   /// Callback to invoke when the [Future] has completed successfully.
   /// Will only be invoked once per [Future] execution.
-  final ValueChanged<T> onData;
+  final ValueChanged<T>? onData;
 
   /// Callback to invoke when the [Future] has completed with an error.
   /// Will only be invoked once per [Future] execution.
   /// Call [VoidCallback] to start executing the [Future] again.
-  final Function(Object, VoidCallback) onError;
+  final Function(Object, VoidCallback)? onError;
 
   const Futuristic({
-    Key key,
-    @required this.futureBuilder,
+    Key? key,
+    required this.futureBuilder,
     this.autoStart = false,
-    this.initialBuilder,
+    required this.initialBuilder,
     this.busyBuilder,
     this.errorBuilder,
     this.dataBuilder,
     this.onData,
     this.onError
-  })  : assert(futureBuilder != null),
-        assert(autoStart ^ (initialBuilder != null)),
-        super(key: key);
+  }) : super(key: key);
 
   @override
   _FuturisticState<T> createState() => _FuturisticState<T>();
 }
 
 class _FuturisticState<T> extends State<Futuristic<T>> {
-  Future<T> _future;
+  Future<T>? _future;
 
   @override
   void initState() {
@@ -89,29 +87,26 @@ class _FuturisticState<T> extends State<Futuristic<T>> {
   }
 
   Widget _handleInitial(BuildContext context) {
-    if (widget.initialBuilder != null) {
-      return widget.initialBuilder(context, _execute);
-    }
-    return _defaultWidget();
+    return widget.initialBuilder(context, _execute);
   }
 
   Widget _handleSnapshot(BuildContext context, AsyncSnapshot<T> snapshot) {
     if (snapshot.hasError) {
-      return _handleError(context, snapshot.error);
+      return _handleError(context, snapshot.error as Object);
     }
-    return _handleData(context, snapshot.data);
+    return _handleData(context, snapshot.data as T);
   }
 
   Widget _handleError(BuildContext context, Object error) {
     if (widget.errorBuilder != null) {
-      return widget.errorBuilder(context, error, _execute);
+      return widget.errorBuilder!(context, error, _execute);
     }
     return _handleInitial(context);
   }
 
   Widget _handleData(BuildContext context, T data) {
     if (widget.dataBuilder != null) {
-      return widget.dataBuilder(context, data);
+      return widget.dataBuilder!(context, data);
     }
     return _handleInitial(context);
   }
@@ -120,25 +115,25 @@ class _FuturisticState<T> extends State<Futuristic<T>> {
     if (widget.busyBuilder == null) {
       return _defaultBusyWidget();
     }
-    return widget.busyBuilder(context);
+    return widget.busyBuilder!(context);
   }
 
   void _execute() {
     setState(() {
       _future = widget.futureBuilder();
-      _future.then(_onData).catchError(_onError);
+      _future!.then(_onData).catchError(_onError);
     });
   }
 
   void _onData(T data) async {
     if (widget.onData != null && _isActive()) {
-      widget.onData(data);
+      widget.onData!(data);
     }
   }
 
   void _onError(Object e) async {
     if (widget.onError != null && _isActive()) {
-      widget.onError(e, _execute);
+      widget.onError!(e, _execute);
     }
   }
 

pubspec.yaml

@@ -5,7 +5,7 @@ author: Martin Rybak <[email protected]>
 homepage: https://github.com/vgventures/futuristic
 
 environment:
-  sdk: ">=2.7.0 <3.0.0"
+  sdk: ">=2.12.0 <3.0.0"
 
 dependencies:
   flutter:
@@ -14,7 +14,11 @@ dependencies:
 dev_dependencies:
   flutter_test:
     sdk: flutter
-  pedantic: ^1.9.0                  # Static analysis rules
+  pedantic: ^1.11.0                  # Static analysis rules
+
+analyzer:
+  enable-experiment:
+  - non-nullabl
 
 # For information on the generic Dart part of this file, see the
 # following page: https://dart.dev/tools/pub/pubspec