diff --git a/veggieseasons/ios/Podfile.lock b/veggieseasons/ios/Podfile.lock
index 9d8f8aac2..524060c9b 100644
--- a/veggieseasons/ios/Podfile.lock
+++ b/veggieseasons/ios/Podfile.lock
@@ -15,8 +15,8 @@ EXTERNAL SOURCES:
 
 SPEC CHECKSUMS:
   Flutter: 50d75fe2f02b26cc09d224853bb45737f8b3214a
-  shared_preferences: af6bfa751691cdc24be3045c43ec037377ada40d
+  shared_preferences: 5033afbb22d372e15aff8ff766df9021b845f273
 
 PODFILE CHECKSUM: aafe91acc616949ddb318b77800a7f51bffa2a4c
 
-COCOAPODS: 1.10.1
+COCOAPODS: 1.11.0
diff --git a/veggieseasons/lib/data/app_state.dart b/veggieseasons/lib/data/app_state.dart
index 193a2911c..34261d64e 100644
--- a/veggieseasons/lib/data/app_state.dart
+++ b/veggieseasons/lib/data/app_state.dart
@@ -26,22 +26,22 @@ class AppState extends ChangeNotifier {
     return _veggies.where((v) => !v.seasons.contains(currentSeason)).toList();
   }
 
-  Veggie getVeggie(int id) => _veggies.singleWhere((v) => v.id == id);
+  Veggie getVeggie(int? id) => _veggies.singleWhere((v) => v.id == id);
 
-  List<Veggie> searchVeggies(String terms) => _veggies
-      .where((v) => v.name.toLowerCase().contains(terms.toLowerCase()))
+  List<Veggie> searchVeggies(String? terms) => _veggies
+      .where((v) => v.name.toLowerCase().contains(terms!.toLowerCase()))
       .toList();
 
-  void setFavorite(int id, bool isFavorite) {
+  void setFavorite(int? id, bool isFavorite) {
     var veggie = getVeggie(id);
     veggie.isFavorite = isFavorite;
     notifyListeners();
   }
 
   /// Used in tests to set the season independent of the current date.
-  static Season debugCurrentSeason;
+  static Season? debugCurrentSeason;
 
-  static Season _getSeasonForDate(DateTime date) {
+  static Season? _getSeasonForDate(DateTime date) {
     if (debugCurrentSeason != null) {
       return debugCurrentSeason;
     }
diff --git a/veggieseasons/lib/data/preferences.dart b/veggieseasons/lib/data/preferences.dart
index f413a2293..67a6dd3fd 100644
--- a/veggieseasons/lib/data/preferences.dart
+++ b/veggieseasons/lib/data/preferences.dart
@@ -16,7 +16,7 @@ class Preferences extends ChangeNotifier {
   static const _preferredCategoriesKey = 'preferredCategories';
 
   // Indicates whether a call to [_loadFromSharedPrefs] is in progress;
-  Future<void> _loading;
+  Future<void>? _loading;
 
   int _desiredCalories = 2000;
 
@@ -79,9 +79,7 @@ class Preferences extends ChangeNotifier {
     if (names != null && names.isNotEmpty) {
       for (final name in names.split(',')) {
         final index = int.tryParse(name) ?? -1;
-        if (VeggieCategory.values[index] != null) {
-          _preferredCategories.add(VeggieCategory.values[index]);
-        }
+        _preferredCategories.add(VeggieCategory.values[index]);
       }
     }
 
diff --git a/veggieseasons/lib/data/veggie.dart b/veggieseasons/lib/data/veggie.dart
index 3161a6534..5b489a5c1 100644
--- a/veggieseasons/lib/data/veggie.dart
+++ b/veggieseasons/lib/data/veggie.dart
@@ -3,7 +3,6 @@
 // found in the LICENSE file.
 
 import 'package:flutter/cupertino.dart';
-import 'package:meta/meta.dart';
 
 enum VeggieCategory {
   allium,
@@ -71,18 +70,18 @@ const Map<Season, String> seasonNames = {
 
 class Veggie {
   Veggie({
-    @required this.id,
-    @required this.name,
-    @required this.imageAssetPath,
-    @required this.category,
-    @required this.shortDescription,
-    @required this.accentColor,
-    @required this.seasons,
-    @required this.vitaminAPercentage,
-    @required this.vitaminCPercentage,
-    @required this.servingSize,
-    @required this.caloriesPerServing,
-    @required this.trivia,
+    required this.id,
+    required this.name,
+    required this.imageAssetPath,
+    required this.category,
+    required this.shortDescription,
+    required this.accentColor,
+    required this.seasons,
+    required this.vitaminAPercentage,
+    required this.vitaminCPercentage,
+    required this.servingSize,
+    required this.caloriesPerServing,
+    required this.trivia,
     this.isFavorite = false,
   });
 
@@ -127,5 +126,5 @@ class Veggie {
   /// A set of trivia questions and answers related to the veggie.
   final List<Trivia> trivia;
 
-  String get categoryName => veggieCategoryNames[category];
+  String? get categoryName => veggieCategoryNames[category];
 }
diff --git a/veggieseasons/lib/main.dart b/veggieseasons/lib/main.dart
index e993ff29d..4d3ee879b 100644
--- a/veggieseasons/lib/main.dart
+++ b/veggieseasons/lib/main.dart
@@ -26,7 +26,7 @@ void main() {
 }
 
 class VeggieApp extends StatefulWidget {
-  const VeggieApp({Key key}) : super(key: key);
+  const VeggieApp({Key? key}) : super(key: key);
 
   @override
   State<StatefulWidget> createState() => _VeggieAppState();
@@ -39,7 +39,7 @@ class _VeggieAppState extends State<VeggieApp> with RestorationMixin {
   String get restorationId => 'wrapper';
 
   @override
-  void restoreState(RestorationBucket oldBucket, bool initialRestore) {
+  void restoreState(RestorationBucket? oldBucket, bool initialRestore) {
     registerForRestoration(_appState, 'state');
   }
 
@@ -77,7 +77,7 @@ class _RestorableAppState extends RestorableListenable<AppState> {
   }
 
   @override
-  AppState fromPrimitives(Object data) {
+  AppState fromPrimitives(Object? data) {
     final appState = AppState();
     final favorites = (data as List<dynamic>).cast<int>();
     for (var id in favorites) {
diff --git a/veggieseasons/lib/screens/details.dart b/veggieseasons/lib/screens/details.dart
index 283fb2c43..a1d343b51 100644
--- a/veggieseasons/lib/screens/details.dart
+++ b/veggieseasons/lib/screens/details.dart
@@ -13,7 +13,7 @@ import 'package:veggieseasons/widgets/close_button.dart';
 import 'package:veggieseasons/widgets/trivia.dart';
 
 class ServingInfoChart extends StatelessWidget {
-  const ServingInfoChart(this.veggie, this.prefs, {Key key}) : super(key: key);
+  const ServingInfoChart(this.veggie, this.prefs, {Key? key}) : super(key: key);
 
   final Veggie veggie;
 
@@ -26,7 +26,7 @@ class ServingInfoChart extends StatelessWidget {
     return FutureBuilder<int>(
       future: targetCalories,
       builder: (context, snapshot) {
-        final target = snapshot?.data ?? 2000;
+        final target = snapshot.data ?? 2000;
         final percent = standardPercentage * 2000 ~/ target;
 
         return Text(
@@ -141,7 +141,7 @@ class ServingInfoChart extends StatelessWidget {
                   builder: (context, snapshot) {
                     return Text(
                       'Percent daily values based on a diet of '
-                      '${snapshot?.data ?? '2,000'} calories.',
+                      '${snapshot.data ?? '2,000'} calories.',
                       style: Styles.detailsServingNoteText(themeData),
                     );
                   },
@@ -156,9 +156,9 @@ class ServingInfoChart extends StatelessWidget {
 }
 
 class InfoView extends StatelessWidget {
-  final int id;
+  final int? id;
 
-  const InfoView(this.id, {Key key}) : super(key: key);
+  const InfoView(this.id, {Key? key}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {
@@ -179,9 +179,9 @@ class InfoView extends StatelessWidget {
                 future: prefs.preferredCategories,
                 builder: (context, snapshot) {
                   return Text(
-                    veggie.categoryName.toUpperCase(),
+                    veggie.categoryName!.toUpperCase(),
                     style: (snapshot.hasData &&
-                            snapshot.data.contains(veggie.category))
+                            snapshot.data!.contains(veggie.category))
                         ? Styles.detailsPreferredCategoryText(themeData)
                         : themeData.textTheme.textStyle,
                   );
@@ -191,7 +191,7 @@ class InfoView extends StatelessWidget {
               for (Season season in veggie.seasons) ...[
                 const SizedBox(width: 12),
                 Padding(
-                  padding: Styles.seasonIconPadding[season],
+                  padding: Styles.seasonIconPadding[season]!,
                   child: Icon(
                     Styles.seasonIconData[season],
                     semanticLabel: seasonNames[season],
@@ -236,17 +236,18 @@ class InfoView extends StatelessWidget {
 }
 
 class DetailsScreen extends StatefulWidget {
-  final int id;
-  final String restorationId;
+  final int? id;
+  final String? restorationId;
 
-  const DetailsScreen({this.id, this.restorationId, Key key}) : super(key: key);
+  const DetailsScreen({this.id, this.restorationId, Key? key})
+      : super(key: key);
 
   static String show(NavigatorState navigator, int veggieId) {
     return navigator.restorablePush<void>(_routeBuilder, arguments: veggieId);
   }
 
-  static Route<void> _routeBuilder(BuildContext context, Object arguments) {
-    final veggieId = arguments as int;
+  static Route<void> _routeBuilder(BuildContext context, Object? arguments) {
+    final veggieId = arguments as int?;
     return CupertinoPageRoute(
       builder: (context) =>
           DetailsScreen(id: veggieId, restorationId: 'details'),
@@ -262,10 +263,10 @@ class _DetailsScreenState extends State<DetailsScreen> with RestorationMixin {
   final RestorableInt _selectedViewIndex = RestorableInt(0);
 
   @override
-  String get restorationId => widget.restorationId;
+  String? get restorationId => widget.restorationId;
 
   @override
-  void restoreState(RestorationBucket oldBucket, bool initialRestore) {
+  void restoreState(RestorationBucket? oldBucket, bool initialRestore) {
     registerForRestoration(_selectedViewIndex, 'tab');
   }
 
diff --git a/veggieseasons/lib/screens/favorites.dart b/veggieseasons/lib/screens/favorites.dart
index 85081d41d..e76aaa84b 100644
--- a/veggieseasons/lib/screens/favorites.dart
+++ b/veggieseasons/lib/screens/favorites.dart
@@ -10,9 +10,9 @@ import 'package:veggieseasons/data/veggie.dart';
 import 'package:veggieseasons/widgets/veggie_headline.dart';
 
 class FavoritesScreen extends StatelessWidget {
-  const FavoritesScreen({this.restorationId, Key key}) : super(key: key);
+  const FavoritesScreen({this.restorationId, Key? key}) : super(key: key);
 
-  final String restorationId;
+  final String? restorationId;
 
   @override
   Widget build(BuildContext context) {
diff --git a/veggieseasons/lib/screens/home.dart b/veggieseasons/lib/screens/home.dart
index 8bcb9eb97..ca2e475cb 100644
--- a/veggieseasons/lib/screens/home.dart
+++ b/veggieseasons/lib/screens/home.dart
@@ -10,9 +10,9 @@ import 'package:veggieseasons/screens/search.dart';
 import 'package:veggieseasons/screens/settings.dart';
 
 class HomeScreen extends StatelessWidget {
-  const HomeScreen({Key key, this.restorationId}) : super(key: key);
+  const HomeScreen({Key? key, this.restorationId}) : super(key: key);
 
-  final String restorationId;
+  final String? restorationId;
 
   @override
   Widget build(BuildContext context) {
diff --git a/veggieseasons/lib/screens/list.dart b/veggieseasons/lib/screens/list.dart
index 1fca2eaa4..aee80d31e 100644
--- a/veggieseasons/lib/screens/list.dart
+++ b/veggieseasons/lib/screens/list.dart
@@ -14,9 +14,9 @@ import 'package:veggieseasons/styles.dart';
 import 'package:veggieseasons/widgets/veggie_card.dart';
 
 class ListScreen extends StatelessWidget {
-  const ListScreen({this.restorationId, Key key}) : super(key: key);
+  const ListScreen({this.restorationId, Key? key}) : super(key: key);
 
-  final String restorationId;
+  final String? restorationId;
 
   Widget _generateVeggieRow(Veggie veggie, Preferences prefs,
       {bool inSeason = true}) {
diff --git a/veggieseasons/lib/screens/search.dart b/veggieseasons/lib/screens/search.dart
index 3a659a7e0..b520d66fa 100644
--- a/veggieseasons/lib/screens/search.dart
+++ b/veggieseasons/lib/screens/search.dart
@@ -11,9 +11,9 @@ import 'package:veggieseasons/data/veggie.dart';
 import 'package:veggieseasons/widgets/veggie_headline.dart';
 
 class SearchScreen extends StatefulWidget {
-  const SearchScreen({this.restorationId, Key key}) : super(key: key);
+  const SearchScreen({this.restorationId, Key? key}) : super(key: key);
 
-  final String restorationId;
+  final String? restorationId;
 
   @override
   _SearchScreenState createState() => _SearchScreenState();
@@ -22,13 +22,13 @@ class SearchScreen extends StatefulWidget {
 class _SearchScreenState extends State<SearchScreen> with RestorationMixin {
   final controller = RestorableTextEditingController();
   final focusNode = FocusNode();
-  String terms;
+  String? terms;
 
   @override
-  String get restorationId => widget.restorationId;
+  String? get restorationId => widget.restorationId;
 
   @override
-  void restoreState(RestorationBucket oldBucket, bool initialRestore) {
+  void restoreState(RestorationBucket? oldBucket, bool initialRestore) {
     registerForRestoration(controller, 'text');
     controller.addListener(_onTextChanged);
     terms = controller.value.text;
diff --git a/veggieseasons/lib/screens/settings.dart b/veggieseasons/lib/screens/settings.dart
index 79585ae44..2e136b65d 100644
--- a/veggieseasons/lib/screens/settings.dart
+++ b/veggieseasons/lib/screens/settings.dart
@@ -13,16 +13,16 @@ import 'package:veggieseasons/widgets/settings_group.dart';
 import 'package:veggieseasons/widgets/settings_item.dart';
 
 class VeggieCategorySettingsScreen extends StatelessWidget {
-  const VeggieCategorySettingsScreen({Key key, this.restorationId})
+  const VeggieCategorySettingsScreen({Key? key, this.restorationId})
       : super(key: key);
 
-  final String restorationId;
+  final String? restorationId;
 
   static String show(NavigatorState navigator) {
     return navigator.restorablePush(_routeBuilder);
   }
 
-  static Route<void> _routeBuilder(BuildContext context, Object argument) {
+  static Route<void> _routeBuilder(BuildContext context, Object? argument) {
     return CupertinoPageRoute(
       builder: (context) =>
           const VeggieCategorySettingsScreen(restorationId: 'category'),
@@ -56,7 +56,7 @@ class VeggieCategorySettingsScreen extends StatelessWidget {
               // otherwise.
               if (snapshot.hasData) {
                 toggle = CupertinoSwitch(
-                  value: snapshot.data.contains(category),
+                  value: snapshot.data!.contains(category),
                   onChanged: (value) {
                     if (value) {
                       model.addPreferredCategory(category);
@@ -73,7 +73,7 @@ class VeggieCategorySettingsScreen extends StatelessWidget {
               }
 
               items.add(SettingsItem(
-                label: veggieCategoryNames[category],
+                label: veggieCategoryNames[category]!,
                 content: toggle,
               ));
             }
@@ -94,9 +94,9 @@ class VeggieCategorySettingsScreen extends StatelessWidget {
 }
 
 class CalorieSettingsScreen extends StatelessWidget {
-  const CalorieSettingsScreen({Key key, this.restorationId}) : super(key: key);
+  const CalorieSettingsScreen({Key? key, this.restorationId}) : super(key: key);
 
-  final String restorationId;
+  final String? restorationId;
 
   static const max = 1000;
   static const min = 2600;
@@ -106,7 +106,7 @@ class CalorieSettingsScreen extends StatelessWidget {
     return navigator.restorablePush(_routeBuilder);
   }
 
-  static Route<void> _routeBuilder(BuildContext context, Object argument) {
+  static Route<void> _routeBuilder(BuildContext context, Object? argument) {
     return CupertinoPageRoute<void>(
       builder: (context) =>
           const CalorieSettingsScreen(restorationId: 'calorie'),
@@ -169,9 +169,9 @@ class CalorieSettingsScreen extends StatelessWidget {
 }
 
 class SettingsScreen extends StatelessWidget {
-  const SettingsScreen({this.restorationId, Key key}) : super(key: key);
+  const SettingsScreen({this.restorationId, Key? key}) : super(key: key);
 
-  final String restorationId;
+  final String? restorationId;
 
   SettingsItem _buildCaloriesItem(BuildContext context, Preferences prefs) {
     return SettingsItem(
diff --git a/veggieseasons/lib/styles.dart b/veggieseasons/lib/styles.dart
index f81d9e2f1..03bfff303 100644
--- a/veggieseasons/lib/styles.dart
+++ b/veggieseasons/lib/styles.dart
@@ -115,7 +115,7 @@ abstract class Styles {
 
   static const appBackground = Color(0xffd0d0d0);
 
-  static Color scaffoldBackground(Brightness brightness) =>
+  static Color? scaffoldBackground(Brightness brightness) =>
       brightness == Brightness.light
           ? CupertinoColors.lightBackgroundGray
           : null;
diff --git a/veggieseasons/lib/widgets/close_button.dart b/veggieseasons/lib/widgets/close_button.dart
index 0c7bde80a..9c7521c6e 100644
--- a/veggieseasons/lib/widgets/close_button.dart
+++ b/veggieseasons/lib/widgets/close_button.dart
@@ -12,10 +12,10 @@ import 'package:veggieseasons/styles.dart';
 class FrostedBox extends StatelessWidget {
   const FrostedBox({
     this.child,
-    Key key,
+    Key? key,
   }) : super(key: key);
 
-  final Widget child;
+  final Widget? child;
 
   @override
   Widget build(BuildContext context) {
@@ -37,18 +37,15 @@ class ColorChangingIcon extends ImplicitlyAnimatedWidget {
     this.icon, {
     this.color = CupertinoColors.black,
     this.size,
-    @required Duration duration,
-    Key key,
-  })  : assert(icon != null),
-        assert(color != null),
-        assert(duration != null),
-        super(key: key, duration: duration);
+    required Duration duration,
+    Key? key,
+  }) : super(key: key, duration: duration);
 
   final Color color;
 
   final IconData icon;
 
-  final double size;
+  final double? size;
 
   @override
   _ColorChangingIconState createState() => _ColorChangingIconState();
@@ -56,7 +53,7 @@ class ColorChangingIcon extends ImplicitlyAnimatedWidget {
 
 class _ColorChangingIconState
     extends AnimatedWidgetBaseState<ColorChangingIcon> {
-  ColorTween _colorTween;
+  ColorTween? _colorTween;
 
   @override
   Widget build(BuildContext context) {
@@ -73,14 +70,14 @@ class _ColorChangingIconState
     _colorTween = visitor(
       _colorTween,
       widget.color,
-      (dynamic value) => ColorTween(begin: value as Color),
-    ) as ColorTween;
+      (dynamic value) => ColorTween(begin: value as Color?),
+    ) as ColorTween?;
   }
 }
 
 /// A simple "close this modal" button that invokes a callback when pressed.
 class CloseButton extends StatefulWidget {
-  const CloseButton(this.onPressed, {Key key}) : super(key: key);
+  const CloseButton(this.onPressed, {Key? key}) : super(key: key);
 
   final VoidCallback onPressed;
 
diff --git a/veggieseasons/lib/widgets/settings_group.dart b/veggieseasons/lib/widgets/settings_group.dart
index 37b11e613..191f3135b 100644
--- a/veggieseasons/lib/widgets/settings_group.dart
+++ b/veggieseasons/lib/widgets/settings_group.dart
@@ -14,7 +14,7 @@ import 'settings_item.dart';
 // See https://github.com/flutter/flutter/projects/29 for more info.
 
 class SettingsGroupHeader extends StatelessWidget {
-  const SettingsGroupHeader(this.title, {Key key}) : super(key: key);
+  const SettingsGroupHeader(this.title, {Key? key}) : super(key: key);
 
   final String title;
 
@@ -35,7 +35,7 @@ class SettingsGroupHeader extends StatelessWidget {
 }
 
 class SettingsGroupFooter extends StatelessWidget {
-  const SettingsGroupFooter(this.title, {Key key}) : super(key: key);
+  const SettingsGroupFooter(this.title, {Key? key}) : super(key: key);
 
   final String title;
 
@@ -55,17 +55,16 @@ class SettingsGroupFooter extends StatelessWidget {
 
 class SettingsGroup extends StatelessWidget {
   SettingsGroup({
-    @required this.items,
+    required this.items,
     this.header,
     this.footer,
-    Key key,
-  })  : assert(items != null),
-        assert(items.isNotEmpty),
+    Key? key,
+  })  : assert(items.isNotEmpty),
         super(key: key);
 
   final List<SettingsItem> items;
-  final Widget header;
-  final Widget footer;
+  final Widget? header;
+  final Widget? footer;
   @override
   Widget build(BuildContext context) {
     var brightness = CupertinoTheme.brightnessOf(context);
@@ -85,7 +84,7 @@ class SettingsGroup extends StatelessWidget {
       child: Column(
         crossAxisAlignment: CrossAxisAlignment.start,
         children: [
-          if (header != null) header,
+          if (header != null) header!,
           Container(
             decoration: BoxDecoration(
               color: CupertinoColors.white,
@@ -105,7 +104,7 @@ class SettingsGroup extends StatelessWidget {
               children: dividedItems,
             ),
           ),
-          if (footer != null) footer,
+          if (footer != null) footer!,
         ],
       ),
     );
diff --git a/veggieseasons/lib/widgets/settings_item.dart b/veggieseasons/lib/widgets/settings_item.dart
index 3a81b90fd..761863e1f 100644
--- a/veggieseasons/lib/widgets/settings_item.dart
+++ b/veggieseasons/lib/widgets/settings_item.dart
@@ -16,7 +16,7 @@ import 'package:veggieseasons/styles.dart';
 typedef SettingsItemCallback = FutureOr<void> Function();
 
 class SettingsNavigationIndicator extends StatelessWidget {
-  const SettingsNavigationIndicator({Key key}) : super(key: key);
+  const SettingsNavigationIndicator({Key? key}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {
@@ -30,12 +30,11 @@ class SettingsNavigationIndicator extends StatelessWidget {
 
 class SettingsIcon extends StatelessWidget {
   const SettingsIcon({
-    @required this.icon,
+    required this.icon,
     this.foregroundColor = CupertinoColors.white,
     this.backgroundColor = CupertinoColors.black,
-    Key key,
-  })  : assert(icon != null),
-        super(key: key);
+    Key? key,
+  }) : super(key: key);
 
   final Color backgroundColor;
   final Color foregroundColor;
@@ -61,20 +60,19 @@ class SettingsIcon extends StatelessWidget {
 
 class SettingsItem extends StatefulWidget {
   const SettingsItem({
-    @required this.label,
+    required this.label,
     this.icon,
     this.content,
     this.subtitle,
     this.onPress,
-    Key key,
-  })  : assert(label != null),
-        super(key: key);
+    Key? key,
+  }) : super(key: key);
 
   final String label;
-  final Widget icon;
-  final Widget content;
-  final String subtitle;
-  final SettingsItemCallback onPress;
+  final Widget? icon;
+  final Widget? content;
+  final String? subtitle;
+  final SettingsItemCallback? onPress;
 
   @override
   State<StatefulWidget> createState() => SettingsItemState();
@@ -97,7 +95,7 @@ class SettingsItemState extends State<SettingsItem> {
             setState(() {
               pressed = true;
             });
-            await widget.onPress();
+            await widget.onPress!();
             Future.delayed(
               const Duration(milliseconds: 150),
               () {
@@ -138,7 +136,7 @@ class SettingsItemState extends State<SettingsItem> {
                                 style: themeData.textTheme.textStyle),
                             const SizedBox(height: 4),
                             Text(
-                              widget.subtitle,
+                              widget.subtitle!,
                               style: Styles.settingsItemSubtitleText(themeData),
                             ),
                           ],
diff --git a/veggieseasons/lib/widgets/trivia.dart b/veggieseasons/lib/widgets/trivia.dart
index 967c11e13..27f16328b 100644
--- a/veggieseasons/lib/widgets/trivia.dart
+++ b/veggieseasons/lib/widgets/trivia.dart
@@ -8,10 +8,10 @@ import 'package:veggieseasons/styles.dart';
 /// Presents a series of trivia questions about a particular widget, and tracks
 /// the user's score.
 class TriviaView extends StatefulWidget {
-  final int id;
-  final String restorationId;
+  final int? id;
+  final String? restorationId;
 
-  const TriviaView({this.id, this.restorationId, Key key}) : super(key: key);
+  const TriviaView({this.id, this.restorationId, Key? key}) : super(key: key);
 
   @override
   _TriviaViewState createState() => _TriviaViewState();
@@ -26,10 +26,10 @@ enum PlayerStatus {
 
 class _TriviaViewState extends State<TriviaView> with RestorationMixin {
   /// Current app state. This is used to fetch veggie data.
-  AppState appState;
+  late AppState appState;
 
   /// The veggie trivia about which to show.
-  Veggie veggie;
+  late Veggie veggie;
 
   /// Index of the current trivia question.
   RestorableInt triviaIndex = RestorableInt(0);
@@ -45,10 +45,10 @@ class _TriviaViewState extends State<TriviaView> with RestorationMixin {
       _RestorablePlayerStatus(PlayerStatus.readyToAnswer);
 
   @override
-  String get restorationId => widget.restorationId;
+  String? get restorationId => widget.restorationId;
 
   @override
-  void restoreState(RestorationBucket oldBucket, bool initialRestore) {
+  void restoreState(RestorationBucket? oldBucket, bool initialRestore) {
     registerForRestoration(triviaIndex, 'index');
     registerForRestoration(score, 'score');
     registerForRestoration(status, 'status');
@@ -234,7 +234,7 @@ class _RestorablePlayerStatus extends RestorableValue<PlayerStatus> {
   }
 
   @override
-  PlayerStatus fromPrimitives(Object data) {
+  PlayerStatus fromPrimitives(Object? data) {
     return PlayerStatus.values[data as int];
   }
 
@@ -244,7 +244,7 @@ class _RestorablePlayerStatus extends RestorableValue<PlayerStatus> {
   }
 
   @override
-  void didUpdateValue(PlayerStatus oldValue) {
+  void didUpdateValue(PlayerStatus? oldValue) {
     notifyListeners();
   }
 }
diff --git a/veggieseasons/lib/widgets/veggie_card.dart b/veggieseasons/lib/widgets/veggie_card.dart
index 9c072e2dc..23bca42d8 100644
--- a/veggieseasons/lib/widgets/veggie_card.dart
+++ b/veggieseasons/lib/widgets/veggie_card.dart
@@ -14,12 +14,12 @@ class FrostyBackground extends StatelessWidget {
     this.color,
     this.intensity = 25,
     this.child,
-    Key key,
+    Key? key,
   }) : super(key: key);
 
-  final Color color;
+  final Color? color;
   final double intensity;
-  final Widget child;
+  final Widget? child;
 
   @override
   Widget build(BuildContext context) {
@@ -41,23 +41,17 @@ class FrostyBackground extends StatelessWidget {
 /// elevation and invoking an optional [onPressed] callback.
 class PressableCard extends StatefulWidget {
   const PressableCard({
-    @required this.child,
+    required this.child,
     this.borderRadius = const BorderRadius.all(Radius.circular(5)),
     this.upElevation = 2,
     this.downElevation = 0,
     this.shadowColor = CupertinoColors.black,
     this.duration = const Duration(milliseconds: 100),
     this.onPressed,
-    Key key,
-  })  : assert(child != null),
-        assert(borderRadius != null),
-        assert(upElevation != null),
-        assert(downElevation != null),
-        assert(shadowColor != null),
-        assert(duration != null),
-        super(key: key);
+    Key? key,
+  }) : super(key: key);
 
-  final VoidCallback onPressed;
+  final VoidCallback? onPressed;
 
   final Widget child;
 
@@ -84,7 +78,7 @@ class _PressableCardState extends State<PressableCard> {
       onTap: () {
         setState(() => cardIsDown = false);
         if (widget.onPressed != null) {
-          widget.onPressed();
+          widget.onPressed!();
         }
       },
       onTapDown: (details) => setState(() => cardIsDown = true),
@@ -107,7 +101,7 @@ class _PressableCardState extends State<PressableCard> {
 
 class VeggieCard extends StatelessWidget {
   const VeggieCard(this.veggie, this.isInSeason, this.isPreferredCategory,
-      {Key key})
+      {Key? key})
       : super(key: key);
 
   /// Veggie to be displayed by the card.
diff --git a/veggieseasons/lib/widgets/veggie_headline.dart b/veggieseasons/lib/widgets/veggie_headline.dart
index 22aa37192..0ff7a909a 100644
--- a/veggieseasons/lib/widgets/veggie_headline.dart
+++ b/veggieseasons/lib/widgets/veggie_headline.dart
@@ -8,17 +8,17 @@ import 'package:veggieseasons/screens/details.dart';
 import 'package:veggieseasons/styles.dart';
 
 class ZoomClipAssetImage extends StatelessWidget {
-  const ZoomClipAssetImage(
-      {@required this.zoom,
-      this.height,
-      this.width,
-      @required this.imageAsset,
-      Key key})
-      : super(key: key);
+  const ZoomClipAssetImage({
+    required this.zoom,
+    this.height,
+    this.width,
+    required this.imageAsset,
+    Key? key,
+  }) : super(key: key);
 
   final double zoom;
-  final double height;
-  final double width;
+  final double? height;
+  final double? width;
   final String imageAsset;
 
   @override
@@ -30,8 +30,8 @@ class ZoomClipAssetImage extends StatelessWidget {
       child: ClipRRect(
         borderRadius: BorderRadius.circular(10),
         child: OverflowBox(
-          maxHeight: height * zoom,
-          maxWidth: width * zoom,
+          maxHeight: height! * zoom,
+          maxWidth: width! * zoom,
           child: Image.asset(
             imageAsset,
             fit: BoxFit.fill,
@@ -45,7 +45,7 @@ class ZoomClipAssetImage extends StatelessWidget {
 class VeggieHeadline extends StatelessWidget {
   final Veggie veggie;
 
-  const VeggieHeadline(this.veggie, {Key key}) : super(key: key);
+  const VeggieHeadline(this.veggie, {Key? key}) : super(key: key);
 
   List<Widget> _buildSeasonDots(List<Season> seasons) {
     var widgets = <Widget>[];
diff --git a/veggieseasons/macos/Podfile.lock b/veggieseasons/macos/Podfile.lock
index e93f18e31..2578211c1 100644
--- a/veggieseasons/macos/Podfile.lock
+++ b/veggieseasons/macos/Podfile.lock
@@ -19,4 +19,4 @@ SPEC CHECKSUMS:
 
 PODFILE CHECKSUM: 6eac6b3292e5142cfc23bdeb71848a40ec51c14c
 
-COCOAPODS: 1.10.1
+COCOAPODS: 1.11.0
diff --git a/veggieseasons/pubspec.lock b/veggieseasons/pubspec.lock
index 2f9ae2a92..82cfc0d28 100644
--- a/veggieseasons/pubspec.lock
+++ b/veggieseasons/pubspec.lock
@@ -21,7 +21,7 @@ packages:
       name: async
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.8.1"
+    version: "2.8.2"
   boolean_selector:
     dependency: transitive
     description:
@@ -35,7 +35,7 @@ packages:
       name: characters
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.0"
+    version: "1.2.0"
   charcode:
     dependency: transitive
     description:
@@ -162,7 +162,7 @@ packages:
       name: matcher
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.12.10"
+    version: "0.12.11"
   meta:
     dependency: transitive
     description:
@@ -239,7 +239,7 @@ packages:
       name: provider
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "5.0.0"
+    version: "6.0.1"
   shared_preferences:
     dependency: "direct main"
     description:
@@ -328,7 +328,7 @@ packages:
       name: test_api
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.4.2"
+    version: "0.4.3"
   typed_data:
     dependency: transitive
     description:
diff --git a/veggieseasons/pubspec.yaml b/veggieseasons/pubspec.yaml
index 523451255..8f3664166 100644
--- a/veggieseasons/pubspec.yaml
+++ b/veggieseasons/pubspec.yaml
@@ -4,7 +4,7 @@ description: An iOS app that shows the fruits and veggies currently in season.
 version: 1.2.0
 
 environment:
-  sdk: ">=2.5.0 <3.0.0"
+  sdk: '>=2.12.0 <3.0.0'
 
 dependencies:
   flutter:
@@ -13,7 +13,7 @@ dependencies:
   cupertino_icons: ^1.0.2
   font_awesome_flutter: ^9.0.0
   intl: ^0.17.0
-  provider: ^5.0.0
+  provider: ^6.0.1
   shared_preferences: ^2.0.5
 
 dev_dependencies: