Add flutter_lints to null_safety (#828)

null_safety/null_safe_app/lib/badapp.dart

@@ -12,13 +12,15 @@ import 'services.dart';
 // uncomment the for-loop and appBar lines below, and note how the new null
 // safety static analysis immediately flags those lines as errors.
 class BadMyApp extends StatelessWidget {
+  const BadMyApp({Key? key}) : super(key: key);
+
   @override
   Widget build(BuildContext context) {
     final localizedAppName = Config.getAppName();
     final temperatures = WeatherService.getTemperatures();
 
     var tempWidgets = [
-      Text('Temperature next 3 days:'),
+      const Text('Temperature next 3 days:'),
       // for (final t in temperatures) Text(t.round().toString()),
     ];
 

null_safety/null_safe_app/lib/goodapp.dart

@@ -7,6 +7,8 @@ import 'package:flutter/material.dart';
 import 'services.dart';
 
 class GoodMyApp extends StatelessWidget {
+  const GoodMyApp({Key? key}) : super(key: key);
+
   @override
   Widget build(BuildContext context) {
     final localizedAppName = Config.getAppName();
@@ -14,13 +16,13 @@ class GoodMyApp extends StatelessWidget {
 
     List<Widget> tempWidgets;
     if (temperatures == null) {
-      tempWidgets = [Text('Temperature: Failed getting forecast :-(')];
+      tempWidgets = [const Text('Temperature: Failed getting forecast :-(')];
     } else {
       // Null safety uses flow analysis. The code checked for null in the branch
       // above, so in this branch it known that temperatures cannot be null.
       // Notice how we access temperatures without getting an analysis error.
       tempWidgets = [
-        Text('Temperature next 3 days:'),
+        const Text('Temperature next 3 days:'),
         for (final t in temperatures)
           // We first use the conditional member access operator to only call
           // round() and toString() if t isn't null. We then test if that

null_safety/null_safe_app/lib/main.dart

@@ -7,5 +7,5 @@ import 'package:flutter/material.dart';
 import 'goodapp.dart';
 
 void main() {
-  runApp(GoodMyApp());
+  runApp(const GoodMyApp());
 }