Add a new null safety example (#562)

experimental/null_safety/null_safe_app/lib/badapp.dart

@@ -0,0 +1,36 @@
+// Copyright 2020, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+
+import 'services.dart';
+
+// This app doesn't work correctly when the services return null. Try to
+// 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 {
+  @override
+  Widget build(BuildContext context) {
+    final localizedAppName = Config.getAppName();
+    final temperatures = WeatherService.getTemperatures();
+
+    var tempWidgets = [
+      Text('Temperature next 3 days:'),
+      // for (final t in temperatures) Text(t.round().toString()),
+    ];
+
+    return MaterialApp(
+      home: Scaffold(
+        // appBar: AppBar(title: Text(localizedAppName)),
+        body: Padding(
+          padding: const EdgeInsets.all(8.0),
+          child: Column(
+            crossAxisAlignment: CrossAxisAlignment.start,
+            children: tempWidgets,
+          ),
+        ),
+      ),
+    );
+  }
+}