Committed null safety changes

Author: SriramKiranSenthilkumar

lib/main.dart

@@ -21,7 +21,7 @@ class ChartApp extends StatelessWidget {
 
 class MyHomePage extends StatefulWidget {
   // ignore: prefer_const_constructors_in_immutables
-  MyHomePage({Key key}) : super(key: key);
+  MyHomePage({Key? key}) : super(key: key);
 
   @override
   _MyHomePageState createState() => _MyHomePageState();
@@ -53,12 +53,12 @@ class _MyHomePageState extends State<MyHomePage> {
                 if (args.pointIndex == 2) {
                   //Tooltip with X and Y positions of data points
                   args.header = 'x : y';
-                  args.text = '${args.locationX.floor()} : ${args.locationY.floor()}';
+                  args.text = '${args.locationX!.floor()} : ${args.locationY!.floor()}';
                 }
                 if(args.pointIndex == 3) {
                   //Tooltip with formatted DateTime values
-                  List<CartesianChartPoint<dynamic>> chartdata = args.dataPoints;
-                  args.header = DateFormat('d MMM yyyy').format(chartdata[3].x);
+                  List<dynamic>? chartdata = args.dataPoints;
+                  args.header = DateFormat('d MMM yyyy').format(chartdata![3].x);
                   args.text = '${chartdata[3].y}';
                 }
               },

pubspec.yaml

@@ -18,7 +18,7 @@ publish_to: 'none' # Remove this line if you wish to publish to pub.dev
 version: 1.0.0+1
 
 environment:
-  sdk: ">=2.7.0 <3.0.0"
+  sdk: ">=2.12.0 <3.0.0"
 
 dependencies:
   flutter:
@@ -28,7 +28,7 @@ dependencies:
   # The following adds the Cupertino Icons font to your application.
   # Use with the CupertinoIcons class for iOS style icons.
   cupertino_icons: ^0.1.3
-  syncfusion_flutter_charts: ^18.1.46
+  syncfusion_flutter_charts: ^19.1.55+1
 
 dev_dependencies:
   flutter_test: