Landing beta changes in master for the new stable release (#747)

infinite_list/lib/main.dart

@@ -32,7 +32,7 @@ class MyHomePage extends StatelessWidget {
       appBar: AppBar(
         title: Text('Infinite List Sample'),
       ),
-      body: Selector<Catalog, int>(
+      body: Selector<Catalog, int?>(
         // Selector is a widget from package:provider. It allows us to listen
         // to only one aspect of a provided value. In this case, we are only
         // listening to the catalog's `itemCount`, because that's all we need

infinite_list/lib/src/api/item.dart

@@ -12,9 +12,9 @@ class Item {
   final String name;
 
   Item({
-    @required this.color,
-    @required this.name,
-    @required this.price,
+    required this.color,
+    required this.name,
+    required this.price,
   });
 
   Item.loading() : this(color: Colors.grey, name: '...', price: 0);

infinite_list/lib/src/api/page.dart

@@ -2,9 +2,6 @@
 // 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 'package:meta/meta.dart';
-
 import 'item.dart';
 
 const int itemsPerPage = 20;
@@ -17,8 +14,8 @@ class ItemPage {
   final bool hasNext;
 
   ItemPage({
-    @required this.items,
-    @required this.startingIndex,
-    @required this.hasNext,
+    required this.items,
+    required this.startingIndex,
+    required this.hasNext,
   });
 }

infinite_list/lib/src/catalog.dart

@@ -32,7 +32,7 @@ class Catalog extends ChangeNotifier {
 
   /// The size of the catalog. This is `null` at first, and only when the user
   /// reaches the end of the catalog, it will hold the actual number.
-  int itemCount;
+  int? itemCount;
 
   /// After the catalog is disposed, we don't allow it to call
   /// [notifyListeners].
@@ -62,7 +62,7 @@ class Catalog extends ChangeNotifier {
 
     // If the corresponding page is already in memory, return immediately.
     if (_pages.containsKey(startingIndex)) {
-      var item = _pages[startingIndex].items[index - startingIndex];
+      var item = _pages[startingIndex]!.items[index - startingIndex];
       return item;
     }
 

infinite_list/lib/src/item_tile.dart

@@ -11,7 +11,7 @@ import 'api/item.dart';
 class ItemTile extends StatelessWidget {
   final Item item;
 
-  ItemTile({@required this.item, Key key}) : super(key: key);
+  ItemTile({required this.item, Key? key}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {
@@ -34,7 +34,7 @@ class ItemTile extends StatelessWidget {
 /// This is the widget responsible for building the "still loading" item
 /// in the list (represented with "..." and a crossed square).
 class LoadingItemTile extends StatelessWidget {
-  const LoadingItemTile({Key key}) : super(key: key);
+  const LoadingItemTile({Key? key}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {