migration of material files to nullsafety (#66633)

packages/flutter/lib/src/material/bottom_sheet_theme.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:ui' show lerpDouble;
 
 import 'package:flutter/foundation.dart';
@@ -41,43 +39,43 @@ class BottomSheetThemeData with Diagnosticable {
   /// Default value for [BottomSheet.backgroundColor].
   ///
   /// If null, [BottomSheet] defaults to [Material]'s default.
-  final Color backgroundColor;
+  final Color? backgroundColor;
 
   /// Default value for [BottomSheet.elevation].
   ///
   /// {@macro flutter.material.material.elevation}
   ///
   /// If null, [BottomSheet] defaults to 0.0.
-  final double elevation;
+  final double? elevation;
 
   /// Value for [BottomSheet.backgroundColor] when the Bottom sheet is presented
   /// as a modal bottom sheet.
-  final Color modalBackgroundColor;
+  final Color? modalBackgroundColor;
 
   /// Value for [BottomSheet.elevation] when the Bottom sheet is presented as a
   /// modal bottom sheet.
-  final double modalElevation;
+  final double? modalElevation;
 
   /// Default value for [BottomSheet.shape].
   ///
   /// If null, no overriding shape is specified for [BottomSheet], so the
   /// [BottomSheet] is rectangular.
-  final ShapeBorder shape;
+  final ShapeBorder? shape;
 
   /// Default value for [BottomSheet.clipBehavior].
   ///
   /// If null, [BottomSheet] uses [Clip.none].
-  final Clip clipBehavior;
+  final Clip? clipBehavior;
 
   /// Creates a copy of this object with the given fields replaced with the
   /// new values.
   BottomSheetThemeData copyWith({
-    Color backgroundColor,
-    double elevation,
-    Color modalBackgroundColor,
-    double modalElevation,
-    ShapeBorder shape,
-    Clip clipBehavior,
+    Color? backgroundColor,
+    double? elevation,
+    Color? modalBackgroundColor,
+    double? modalElevation,
+    ShapeBorder? shape,
+    Clip? clipBehavior,
   }) {
     return BottomSheetThemeData(
       backgroundColor: backgroundColor ?? this.backgroundColor,
@@ -94,7 +92,7 @@ class BottomSheetThemeData with Diagnosticable {
   /// If both arguments are null then null is returned.
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static BottomSheetThemeData lerp(BottomSheetThemeData a, BottomSheetThemeData b, double t) {
+  static BottomSheetThemeData? lerp(BottomSheetThemeData? a, BottomSheetThemeData? b, double t) {
     assert(t != null);
     if (a == null && b == null)
       return null;

packages/flutter/lib/src/material/colors.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:ui' show Color;
 
 import 'package:flutter/painting.dart';
@@ -27,34 +25,34 @@ class MaterialColor extends ColorSwatch<int> {
   const MaterialColor(int primary, Map<int, Color> swatch) : super(primary, swatch);
 
   /// The lightest shade.
-  Color get shade50 => this[50];
+  Color get shade50 => this[50]!;
 
   /// The second lightest shade.
-  Color get shade100 => this[100];
+  Color get shade100 => this[100]!;
 
   /// The third lightest shade.
-  Color get shade200 => this[200];
+  Color get shade200 => this[200]!;
 
   /// The fourth lightest shade.
-  Color get shade300 => this[300];
+  Color get shade300 => this[300]!;
 
   /// The fifth lightest shade.
-  Color get shade400 => this[400];
+  Color get shade400 => this[400]!;
 
   /// The default shade.
-  Color get shade500 => this[500];
+  Color get shade500 => this[500]!;
 
   /// The fourth darkest shade.
-  Color get shade600 => this[600];
+  Color get shade600 => this[600]!;
 
   /// The third darkest shade.
-  Color get shade700 => this[700];
+  Color get shade700 => this[700]!;
 
   /// The second darkest shade.
-  Color get shade800 => this[800];
+  Color get shade800 => this[800]!;
 
   /// The darkest shade.
-  Color get shade900 => this[900];
+  Color get shade900 => this[900]!;
 }
 
 /// Defines a single accent color as well a swatch of four shades of the
@@ -75,19 +73,19 @@ class MaterialAccentColor extends ColorSwatch<int> {
   const MaterialAccentColor(int primary, Map<int, Color> swatch) : super(primary, swatch);
 
   /// The lightest shade.
-  Color get shade50 => this[50];
+  Color get shade50 => this[50]!;
 
   /// The second lightest shade.
-  Color get shade100 => this[100];
+  Color get shade100 => this[100]!;
 
   /// The default shade.
-  Color get shade200 => this[200];
+  Color get shade200 => this[200]!;
 
   /// The second darkest shade.
-  Color get shade400 => this[400];
+  Color get shade400 => this[400]!;
 
   /// The darkest shade.
-  Color get shade700 => this[700];
+  Color get shade700 => this[700]!;
 }
 
 /// [Color] and [ColorSwatch] constants which represent Material design's

packages/flutter/lib/src/material/constants.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/painting.dart';
 
 /// The minimum dimension of any interactive region according to Material

packages/flutter/lib/src/material/curves.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/animation.dart';
 
 // The easing curves of the Material Library

packages/flutter/lib/src/material/floating_action_button_theme.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:ui' show lerpDouble;
 
 import 'package:flutter/foundation.dart';
@@ -48,63 +46,63 @@ class FloatingActionButtonThemeData with Diagnosticable {
 
   /// Color to be used for the unselected, enabled [FloatingActionButton]'s
   /// foreground.
-  final Color foregroundColor;
+  final Color? foregroundColor;
 
   /// Color to be used for the unselected, enabled [FloatingActionButton]'s
   /// background.
-  final Color backgroundColor;
+  final Color? backgroundColor;
 
   /// The color to use for filling the button when the button has input focus.
-  final Color focusColor;
+  final Color? focusColor;
 
   /// The color to use for filling the button when the button has a pointer
   /// hovering over it.
-  final Color hoverColor;
+  final Color? hoverColor;
 
   /// The splash color for this [FloatingActionButton]'s [InkWell].
-  final Color splashColor;
+  final Color? splashColor;
 
   /// The z-coordinate to be used for the unselected, enabled
   /// [FloatingActionButton]'s elevation foreground.
-  final double elevation;
+  final double? elevation;
 
   /// The z-coordinate at which to place this button relative to its parent when
   /// the button has the input focus.
   ///
   /// This controls the size of the shadow below the floating action button.
-  final double focusElevation;
+  final double? focusElevation;
 
   /// The z-coordinate at which to place this button relative to its parent when
   /// the button is enabled and has a pointer hovering over it.
   ///
   /// This controls the size of the shadow below the floating action button.
-  final double hoverElevation;
+  final double? hoverElevation;
 
   /// The z-coordinate to be used for the disabled [FloatingActionButton]'s
   /// elevation foreground.
-  final double disabledElevation;
+  final double? disabledElevation;
 
   /// The z-coordinate to be used for the selected, enabled
   /// [FloatingActionButton]'s elevation foreground.
-  final double highlightElevation;
+  final double? highlightElevation;
 
   /// The shape to be used for the floating action button's [Material].
-  final ShapeBorder shape;
+  final ShapeBorder? shape;
 
   /// Creates a copy of this object with the given fields replaced with the
   /// new values.
   FloatingActionButtonThemeData copyWith({
-    Color foregroundColor,
-    Color backgroundColor,
-    Color focusColor,
-    Color hoverColor,
-    Color splashColor,
-    double elevation,
-    double focusElevation,
-    double hoverElevation,
-    double disabledElevation,
-    double highlightElevation,
-    ShapeBorder shape,
+    Color? foregroundColor,
+    Color? backgroundColor,
+    Color? focusColor,
+    Color? hoverColor,
+    Color? splashColor,
+    double? elevation,
+    double? focusElevation,
+    double? hoverElevation,
+    double? disabledElevation,
+    double? highlightElevation,
+    ShapeBorder? shape,
   }) {
     return FloatingActionButtonThemeData(
       foregroundColor: foregroundColor ?? this.foregroundColor,
@@ -126,7 +124,7 @@ class FloatingActionButtonThemeData with Diagnosticable {
   /// If both arguments are null then null is returned.
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static FloatingActionButtonThemeData lerp(FloatingActionButtonThemeData a, FloatingActionButtonThemeData b, double t) {
+  static FloatingActionButtonThemeData? lerp(FloatingActionButtonThemeData? a, FloatingActionButtonThemeData? b, double t) {
     assert(t != null);
     if (a == null && b == null)
       return null;

packages/flutter/lib/src/material/flutter_logo.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/widgets.dart';
 
 /// The Flutter logo, in widget form. This widget respects the [IconTheme].
@@ -22,7 +20,7 @@ class FlutterLogo extends StatelessWidget {
   /// The [textColor], [style], [duration], and [curve] arguments must not be
   /// null.
   const FlutterLogo({
-    Key key,
+    Key? key,
     this.size,
     this.textColor = const Color(0xFF757575),
     this.style = FlutterLogoStyle.markOnly,
@@ -41,7 +39,7 @@ class FlutterLogo extends StatelessWidget {
   /// Defaults to the current [IconTheme] size, if any. If there is no
   /// [IconTheme], or it does not specify an explicit size, then it defaults to
   /// 24.0.
-  final double size;
+  final double? size;
 
   /// The color used to paint the "Flutter" text on the logo, if [style] is
   /// [FlutterLogoStyle.horizontal] or [FlutterLogoStyle.stacked].
@@ -64,7 +62,7 @@ class FlutterLogo extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final IconThemeData iconTheme = IconTheme.of(context);
-    final double iconSize = size ?? iconTheme.size;
+    final double? iconSize = size ?? iconTheme.size;
     return AnimatedContainer(
       width: iconSize,
       height: iconSize,

packages/flutter/lib/src/material/grid_tile.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/widgets.dart';
 
 /// A tile in a material design grid list.
@@ -23,22 +21,22 @@ class GridTile extends StatelessWidget {
   ///
   /// Must have a child. Does not typically have both a header and a footer.
   const GridTile({
-    Key key,
+    Key? key,
     this.header,
     this.footer,
-    @required this.child,
+    required this.child,
   }) : assert(child != null),
        super(key: key);
 
   /// The widget to show over the top of this grid tile.
   ///
   /// Typically a [GridTileBar].
-  final Widget header;
+  final Widget? header;
 
   /// The widget to show over the bottom of this grid tile.
   ///
   /// Typically a [GridTileBar].
-  final Widget footer;
+  final Widget? footer;
 
   /// The widget that fills the tile.
   ///
@@ -60,14 +58,14 @@ class GridTile extends StatelessWidget {
             top: 0.0,
             left: 0.0,
             right: 0.0,
-            child: header,
+            child: header!,
           ),
         if (footer != null)
           Positioned(
             left: 0.0,
             bottom: 0.0,
             right: 0.0,
-            child: footer,
+            child: footer!,
           ),
       ],
     );

packages/flutter/lib/src/material/icons.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/widgets.dart';
 
 /// Identifiers for the supported material design icons.

packages/flutter/lib/src/material/material_state.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:ui' show Color;
 
 import 'package:flutter/foundation.dart';
@@ -76,7 +74,7 @@ enum MaterialState {
 
 /// Signature for the function that returns a value of type `T` based on a given
 /// set of states.
-typedef MaterialPropertyResolver<T> = T Function(Set<MaterialState> states);
+typedef MaterialPropertyResolver<T> = T? Function(Set<MaterialState> states);
 
 /// Defines a [Color] that is also a [MaterialStateProperty].
 ///
@@ -139,7 +137,7 @@ abstract class MaterialStateColor extends Color implements MaterialStateProperty
   /// Returns a [Color] that's to be used when a Material component is in the
   /// specified state.
   @override
-  Color resolve(Set<MaterialState> states);
+  Color? resolve(Set<MaterialState> states);
 }
 
 /// A [MaterialStateColor] created from a [MaterialPropertyResolver<Color>]
@@ -150,7 +148,7 @@ abstract class MaterialStateColor extends Color implements MaterialStateProperty
 ///
 /// Used by [MaterialStateColor.resolveWith].
 class _MaterialStateColor extends MaterialStateColor {
-  _MaterialStateColor(this._resolve) : super(_resolve(_defaultStates).value);
+  _MaterialStateColor(this._resolve) : super(_resolve(_defaultStates)!.value);
 
   final MaterialPropertyResolver<Color> _resolve;
 
@@ -158,7 +156,7 @@ class _MaterialStateColor extends MaterialStateColor {
   static const Set<MaterialState> _defaultStates = <MaterialState>{};
 
   @override
-  Color resolve(Set<MaterialState> states) => _resolve(states);
+  Color? resolve(Set<MaterialState> states) => _resolve(states);
 }
 
 /// Defines a [MouseCursor] whose value depends on a set of [MaterialState]s which
@@ -224,7 +222,7 @@ abstract class MaterialStateMouseCursor extends MouseCursor implements MaterialS
   @protected
   @override
   MouseCursorSession createSession(int device) {
-    return resolve(<MaterialState>{}).createSession(device);
+    return resolve(<MaterialState>{})!.createSession(device);
   }
 
   /// Returns a [MouseCursor] that's to be used when a Material component is in
@@ -232,7 +230,7 @@ abstract class MaterialStateMouseCursor extends MouseCursor implements MaterialS
   ///
   /// This method should never return null.
   @override
-  MouseCursor resolve(Set<MaterialState> states);
+  MouseCursor? resolve(Set<MaterialState> states);
 
   /// A mouse cursor for clickable material widgets, which resolves differently
   /// when the widget is disabled.
@@ -263,9 +261,9 @@ abstract class MaterialStateMouseCursor extends MouseCursor implements MaterialS
 
 class _EnabledAndDisabledMouseCursor extends MaterialStateMouseCursor {
   const _EnabledAndDisabledMouseCursor({
-    this.enabledCursor,
-    this.disabledCursor,
-    this.name,
+    required this.enabledCursor,
+    required this.disabledCursor,
+    required this.name,
   });
 
   final MouseCursor enabledCursor;
@@ -349,7 +347,7 @@ abstract class MaterialStateProperty<T> {
   /// Widgets like [TextButton] and [ElevatedButton] apply this method to their
   /// current [MaterialState]s to compute colors and other visual parameters
   /// at build time.
-  T resolve(Set<MaterialState> states);
+  T? resolve(Set<MaterialState> states);
 
   /// Resolves the value for the given set of states if `value` is a
   /// [MaterialStateProperty], otherwise returns the value itself.
@@ -357,9 +355,9 @@ abstract class MaterialStateProperty<T> {
   /// This is useful for widgets that have parameters which can optionally be a
   /// [MaterialStateProperty]. For example, [InkWell.mouseCursor] can be a
   /// [MouseCursor] or a [MaterialStateProperty<MouseCursor>].
-  static T resolveAs<T>(T value, Set<MaterialState> states) {
+  static T? resolveAs<T>(T? value, Set<MaterialState> states) {
     if (value is MaterialStateProperty<T>) {
-      final MaterialStateProperty<T> property = value;
+      final MaterialStateProperty<T> property = value as MaterialStateProperty<T>;
       return property.resolve(states);
     }
     return value;
@@ -371,7 +369,7 @@ abstract class MaterialStateProperty<T> {
 
   /// Convenience method for creating a [MaterialStateProperty] that resolves
   /// to a single value for all states.
-  static MaterialStateProperty<T> all<T>(T value) => _MaterialStatePropertyAll<T>(value);
+  static MaterialStateProperty<T> all<T>(T? value) => _MaterialStatePropertyAll<T>(value);
 }
 
 class _MaterialStatePropertyWith<T> implements MaterialStateProperty<T> {
@@ -380,16 +378,16 @@ class _MaterialStatePropertyWith<T> implements MaterialStateProperty<T> {
   final MaterialPropertyResolver<T> _resolve;
 
   @override
-  T resolve(Set<MaterialState> states) => _resolve(states);
+  T? resolve(Set<MaterialState> states) => _resolve(states);
 }
 
 class _MaterialStatePropertyAll<T> implements MaterialStateProperty<T> {
   _MaterialStatePropertyAll(this.value);
 
-  final T value;
+  final T? value;
 
   @override
-  T resolve(Set<MaterialState> states) => value;
+  T? resolve(Set<MaterialState> states) => value;
 
   @override
   String toString() => 'MaterialStateProperty.all($value)';

packages/flutter/lib/src/material/toggleable.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/animation.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/gestures.dart';
@@ -32,15 +30,15 @@ abstract class RenderToggleable extends RenderConstrainedBox {
   /// The [activeColor], and [inactiveColor] arguments must not be
   /// null. The [value] can only be null if tristate is true.
   RenderToggleable({
-    @required bool value,
+    required bool? value,
     bool tristate = false,
-    @required Color activeColor,
-    @required Color inactiveColor,
-    Color hoverColor,
-    Color focusColor,
-    ValueChanged<bool> onChanged,
-    BoxConstraints additionalConstraints,
-    @required TickerProvider vsync,
+    required Color activeColor,
+    required Color inactiveColor,
+    Color? hoverColor,
+    Color? focusColor,
+    ValueChanged<bool?>? onChanged,
+    required BoxConstraints additionalConstraints,
+    required TickerProvider vsync,
     bool hasFocus = false,
     bool hovering = false,
   }) : assert(tristate != null),
@@ -110,7 +108,7 @@ abstract class RenderToggleable extends RenderConstrainedBox {
   /// animation reaches either 0.0 or 1.0.
   @protected
   AnimationController get positionController => _positionController;
-  AnimationController _positionController;
+  late AnimationController _positionController;
 
   /// The visual value of the control.
   ///
@@ -121,7 +119,7 @@ abstract class RenderToggleable extends RenderConstrainedBox {
   /// to active (or vice versa), [value] is the target value and this animation
   /// gradually updates from 0.0 to 1.0 (or vice versa).
   CurvedAnimation get position => _position;
-  CurvedAnimation _position;
+  late CurvedAnimation _position;
 
   /// Used by subclasses to control the radial reaction animation.
   ///
@@ -132,8 +130,8 @@ abstract class RenderToggleable extends RenderConstrainedBox {
   /// reaction.
   @protected
   AnimationController get reactionController => _reactionController;
-  AnimationController _reactionController;
-  Animation<double> _reaction;
+  late AnimationController _reactionController;
+  late Animation<double> _reaction;
 
   /// Used by subclasses to control the radial reaction's opacity animation for
   /// [hasFocus] changes.
@@ -146,8 +144,8 @@ abstract class RenderToggleable extends RenderConstrainedBox {
   /// reaction.
   @protected
   AnimationController get reactionFocusFadeController => _reactionFocusFadeController;
-  AnimationController _reactionFocusFadeController;
-  Animation<double> _reactionFocusFade;
+  late AnimationController _reactionFocusFadeController;
+  late Animation<double> _reactionFocusFade;
 
   /// Used by subclasses to control the radial reaction's opacity animation for
   /// [hovering] changes.
@@ -160,8 +158,8 @@ abstract class RenderToggleable extends RenderConstrainedBox {
   /// reaction.
   @protected
   AnimationController get reactionHoverFadeController => _reactionHoverFadeController;
-  AnimationController _reactionHoverFadeController;
-  Animation<double> _reactionHoverFade;
+  late AnimationController _reactionHoverFadeController;
+  late Animation<double> _reactionHoverFade;
 
   /// True if this toggleable has the input focus.
   bool get hasFocus => _hasFocus;
@@ -216,9 +214,9 @@ abstract class RenderToggleable extends RenderConstrainedBox {
   /// When the value changes, this object starts the [positionController] and
   /// [position] animations to animate the visual appearance of the control to
   /// the new value.
-  bool get value => _value;
-  bool _value;
-  set value(bool value) {
+  bool? get value => _value;
+  bool? _value;
+  set value(bool? value) {
     assert(tristate || value != null);
     if (value == _value)
       return;
@@ -323,9 +321,9 @@ abstract class RenderToggleable extends RenderConstrainedBox {
   /// that is displayed when the toggleable is toggled by a tap.
   ///
   /// Defaults to the [activeColor] at alpha [kRadialReactionAlpha].
-  Color get reactionColor => _reactionColor;
-  Color _reactionColor;
-  set reactionColor(Color value) {
+  Color? get reactionColor => _reactionColor;
+  Color? _reactionColor;
+  set reactionColor(Color? value) {
     assert(value != null);
     if (value == _reactionColor)
       return;
@@ -342,9 +340,9 @@ abstract class RenderToggleable extends RenderConstrainedBox {
   /// callback is non-null. If the callback is null, then the control is
   /// disabled, and non-interactive. A disabled checkbox, for example, is
   /// displayed using a grey color and its value cannot be changed.
-  ValueChanged<bool> get onChanged => _onChanged;
-  ValueChanged<bool> _onChanged;
-  set onChanged(ValueChanged<bool> value) {
+  ValueChanged<bool?>? get onChanged => _onChanged;
+  ValueChanged<bool?>? _onChanged;
+  set onChanged(ValueChanged<bool?>? value) {
     if (value == _onChanged)
       return;
     final bool wasInteractive = isInteractive;
@@ -363,8 +361,8 @@ abstract class RenderToggleable extends RenderConstrainedBox {
   /// grey color and its value cannot be changed.
   bool get isInteractive => onChanged != null;
 
-  TapGestureRecognizer _tap;
-  Offset _downPosition;
+  late TapGestureRecognizer _tap;
+  Offset? _downPosition;
 
   @override
   void attach(PipelineOwner owner) {
@@ -410,13 +408,13 @@ abstract class RenderToggleable extends RenderConstrainedBox {
       return;
     switch (value) {
       case false:
-        onChanged(true);
+        onChanged!(true);
         break;
       case true:
-        onChanged(tristate ? null : false);
+        onChanged!(tristate ? null : false);
         break;
-      default: // case null:
-        onChanged(false);
+      case null:
+        onChanged!(false);
         break;
     }
     sendSemanticsEvent(const TapSemanticEvent());
@@ -457,8 +455,8 @@ abstract class RenderToggleable extends RenderConstrainedBox {
           Color.lerp(activeColor.withAlpha(kRadialReactionAlpha), hoverColor, _reactionHoverFade.value),
           focusColor,
           _reactionFocusFade.value,
-        );
-      final Offset center = Offset.lerp(_downPosition ?? origin, origin, _reaction.value);
+        )!;
+      final Offset center = Offset.lerp(_downPosition ?? origin, origin, _reaction.value)!;
       final double reactionRadius = hasFocus || hovering
           ? kRadialReactionRadius
           : _kRadialReactionRadiusTween.evaluate(_reaction);

packages/flutter/lib/src/material/typography.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/foundation.dart';
 import 'package:flutter/painting.dart';
 
@@ -117,12 +115,12 @@ class Typography with Diagnosticable {
   /// The default values for [englishLike], [dense], and [tall] are
   /// [englishLike2014], [dense2014], and [tall2014].
   factory Typography.material2014({
-    TargetPlatform platform = TargetPlatform.android,
-    TextTheme black,
-    TextTheme white,
-    TextTheme englishLike,
-    TextTheme dense,
-    TextTheme tall,
+    TargetPlatform? platform = TargetPlatform.android,
+    TextTheme? black,
+    TextTheme? white,
+    TextTheme? englishLike,
+    TextTheme? dense,
+    TextTheme? tall,
   }) {
     assert(platform != null || (black != null && white != null));
     return Typography._withPlatform(
@@ -145,12 +143,12 @@ class Typography with Diagnosticable {
   /// The default values for [englishLike], [dense], and [tall] are
   /// [englishLike2018], [dense2018], and [tall2018].
   factory Typography.material2018({
-    TargetPlatform platform = TargetPlatform.android,
-    TextTheme black,
-    TextTheme white,
-    TextTheme englishLike,
-    TextTheme dense,
-    TextTheme tall,
+    TargetPlatform? platform = TargetPlatform.android,
+    TextTheme? black,
+    TextTheme? white,
+    TextTheme? englishLike,
+    TextTheme? dense,
+    TextTheme? tall,
   }) {
     assert(platform != null || (black != null && white != null));
     return Typography._withPlatform(
@@ -163,9 +161,9 @@ class Typography with Diagnosticable {
   }
 
   factory Typography._withPlatform(
-    TargetPlatform platform,
-    TextTheme black,
-    TextTheme white,
+    TargetPlatform? platform,
+    TextTheme? black,
+    TextTheme? white,
     TextTheme englishLike,
     TextTheme dense,
     TextTheme tall,
@@ -193,8 +191,10 @@ class Typography with Diagnosticable {
         black ??= blackHelsinki;
         white ??= whiteHelsinki;
         break;
+      case null:
+        break;
     }
-    return Typography._(black, white, englishLike, dense, tall);
+    return Typography._(black!, white!, englishLike, dense, tall);
   }
 
   const Typography._(this.black, this.white, this.englishLike, this.dense, this.tall)
@@ -269,17 +269,16 @@ class Typography with Diagnosticable {
       case ScriptCategory.tall:
         return tall;
     }
-    return null;
   }
 
   /// Creates a copy of this [Typography] with the given fields
   /// replaced by the non-null parameter values.
   Typography copyWith({
-    TextTheme black,
-    TextTheme white,
-    TextTheme englishLike,
-    TextTheme dense,
-    TextTheme tall,
+    TextTheme? black,
+    TextTheme? white,
+    TextTheme? englishLike,
+    TextTheme? dense,
+    TextTheme? tall,
   }) {
     return Typography._(
       black ?? this.black,