migrate some material files to nullsafty (#66858)

* migrate some material files to nullsafty

* address review comments

packages/flutter/lib/src/material/card_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';
@@ -46,44 +44,44 @@ class CardTheme with Diagnosticable {
   /// Default value for [Card.clipBehavior].
   ///
   /// If null, [Card] uses [Clip.none].
-  final Clip clipBehavior;
+  final Clip? clipBehavior;
 
   /// Default value for [Card.color].
   ///
   /// If null, [Card] uses [ThemeData.cardColor].
-  final Color color;
+  final Color? color;
 
   /// Default value for [Card.shadowColor].
   ///
   /// If null, [Card] defaults to fully opaque black.
-  final Color shadowColor;
+  final Color? shadowColor;
 
   /// Default value for [Card.elevation].
   ///
   /// If null, [Card] uses a default of 1.0.
-  final double elevation;
+  final double? elevation;
 
   /// Default value for [Card.margin].
   ///
   /// If null, [Card] uses a default margin of 4.0 logical pixels on all sides:
   /// `EdgeInsets.all(4.0)`.
-  final EdgeInsetsGeometry margin;
+  final EdgeInsetsGeometry? margin;
 
   /// Default value for [Card.shape].
   ///
   /// If null, [Card] then uses a [RoundedRectangleBorder] with a circular
   /// corner radius of 4.0.
-  final ShapeBorder shape;
+  final ShapeBorder? shape;
 
   /// Creates a copy of this object with the given fields replaced with the
   /// new values.
   CardTheme copyWith({
-    Clip clipBehavior,
-    Color color,
-    Color shadowColor,
-    double elevation,
-    EdgeInsetsGeometry margin,
-    ShapeBorder shape,
+    Clip? clipBehavior,
+    Color? color,
+    Color? shadowColor,
+    double? elevation,
+    EdgeInsetsGeometry? margin,
+    ShapeBorder? shape,
   }) {
     return CardTheme(
       clipBehavior: clipBehavior ?? this.clipBehavior,
@@ -97,7 +95,7 @@ class CardTheme with Diagnosticable {
 
   /// The [ThemeData.cardTheme] property of the ambient [Theme].
   static CardTheme of(BuildContext context) {
-    return Theme.of(context).cardTheme;
+    return Theme.of(context)!.cardTheme;
   }
 
   /// Linearly interpolate between two Card themes.
@@ -105,7 +103,7 @@ class CardTheme with Diagnosticable {
   /// The argument `t` must not be null.
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static CardTheme lerp(CardTheme a, CardTheme b, double t) {
+  static CardTheme lerp(CardTheme? a, CardTheme? b, double t) {
     assert(t != null);
     return CardTheme(
       clipBehavior: t < 0.5 ? a?.clipBehavior : b?.clipBehavior,

packages/flutter/lib/src/material/debug.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/widgets.dart';
 

packages/flutter/lib/src/material/elevation_overlay.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:math' as math;
 
 import 'package:flutter/widgets.dart';
@@ -45,7 +43,7 @@ class ElevationOverlay {
   ///  * <https://material.io/design/color/dark-theme.html>, which specifies how
   ///    the overlay should be applied.
   static Color applyOverlay(BuildContext context, Color color, double elevation) {
-    final ThemeData theme = Theme.of(context);
+    final ThemeData theme = Theme.of(context)!;
     if (elevation > 0.0 &&
         theme.applyElevationOverlayColor &&
         theme.brightness == Brightness.dark &&
@@ -63,7 +61,7 @@ class ElevationOverlay {
   ///  * https://material.io/design/color/dark-theme.html#properties which
   ///    specifies the exact overlay values for a given elevation.
   static Color overlayColor(BuildContext context, double elevation) {
-    final ThemeData theme = Theme.of(context);
+    final ThemeData theme = Theme.of(context)!;
     // Compute the opacity for the given elevation
     // This formula matches the values in the spec:
     // https://material.io/design/color/dark-theme.html#properties

packages/flutter/lib/src/material/feedback.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/rendering.dart';
 import 'package:flutter/semantics.dart';
 import 'package:flutter/services.dart';
@@ -94,7 +92,7 @@ class Feedback {
   ///  * [wrapForTap] to trigger platform-specific feedback before executing a
   ///    [GestureTapCallback].
   static Future<void> forTap(BuildContext context) async {
-    context.findRenderObject().sendSemanticsEvent(const TapSemanticEvent());
+    context.findRenderObject()!.sendSemanticsEvent(const TapSemanticEvent());
     switch (_platform(context)) {
       case TargetPlatform.android:
       case TargetPlatform.fuchsia:
@@ -104,10 +102,7 @@ class Feedback {
       case TargetPlatform.macOS:
       case TargetPlatform.windows:
         return Future<void>.value();
-        break;
     }
-    assert(false, 'Unhandled TargetPlatform ${_platform(context)}');
-    return Future<void>.value();
   }
 
   /// Wraps a [GestureTapCallback] to provide platform specific feedback for a
@@ -120,7 +115,7 @@ class Feedback {
   ///
   ///  * [forTap] to just trigger the platform-specific feedback without wrapping
   ///    a [GestureTapCallback].
-  static GestureTapCallback wrapForTap(GestureTapCallback callback, BuildContext context) {
+  static GestureTapCallback? wrapForTap(GestureTapCallback? callback, BuildContext context) {
     if (callback == null)
       return null;
     return () {
@@ -139,7 +134,7 @@ class Feedback {
   ///  * [wrapForLongPress] to trigger platform-specific feedback before
   ///    executing a [GestureLongPressCallback].
   static Future<void> forLongPress(BuildContext context) {
-    context.findRenderObject().sendSemanticsEvent(const LongPressSemanticsEvent());
+    context.findRenderObject()!.sendSemanticsEvent(const LongPressSemanticsEvent());
     switch (_platform(context)) {
       case TargetPlatform.android:
       case TargetPlatform.fuchsia:
@@ -149,10 +144,7 @@ class Feedback {
       case TargetPlatform.macOS:
       case TargetPlatform.windows:
         return Future<void>.value();
-        break;
     }
-    assert(false, 'Unhandled TargetPlatform ${_platform(context)}');
-    return Future<void>.value();
   }
 
   /// Wraps a [GestureLongPressCallback] to provide platform specific feedback
@@ -166,7 +158,7 @@ class Feedback {
   ///
   ///  * [forLongPress] to just trigger the platform-specific feedback without
   ///    wrapping a [GestureLongPressCallback].
-  static GestureLongPressCallback wrapForLongPress(GestureLongPressCallback callback, BuildContext context) {
+  static GestureLongPressCallback? wrapForLongPress(GestureLongPressCallback? callback, BuildContext context) {
     if (callback == null)
       return null;
     return () {
@@ -175,5 +167,5 @@ class Feedback {
     };
   }
 
-  static TargetPlatform _platform(BuildContext context) => Theme.of(context).platform;
+  static TargetPlatform _platform(BuildContext context) => Theme.of(context)!.platform;
 }

packages/flutter/lib/src/material/material_localizations.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/widgets.dart';
 
@@ -135,7 +133,7 @@ abstract class MaterialLocalizations {
   /// there are, e.g. 'Tab 1 of 2' in United States English.
   ///
   /// `tabIndex` and `tabCount` must be greater than or equal to one.
-  String tabLabel({ int tabIndex, int tabCount });
+  String tabLabel({ required int tabIndex, required int tabCount });
 
   /// Title for the [PaginatedDataTable]'s selected row count header.
   String selectedRowCountTitle(int selectedRowCount);
@@ -319,7 +317,7 @@ abstract class MaterialLocalizations {
   ///
   /// See also:
   ///   * [formatCompactDate], which will convert a [DateTime] into a string in the compact format.
-  DateTime parseCompactDate(String inputString);
+  DateTime? parseCompactDate(String? inputString);
 
   /// List of week day names in narrow format, usually 1- or 2-letter
   /// abbreviations of full names.
@@ -505,7 +503,7 @@ abstract class MaterialLocalizations {
   /// ```dart
   /// tooltip: MaterialLocalizations.of(context).backButtonTooltip,
   /// ```
-  static MaterialLocalizations of(BuildContext context) {
+  static MaterialLocalizations? of(BuildContext context) {
     return Localizations.of<MaterialLocalizations>(context, MaterialLocalizations);
   }
 }
@@ -696,24 +694,28 @@ class DefaultMaterialLocalizations implements MaterialLocalizations {
   }
 
   @override
-  DateTime parseCompactDate(String inputString) {
+  DateTime? parseCompactDate(String? inputString) {
+    if (inputString == null) {
+      return null;
+    }
+
     // Assumes US mm/dd/yyyy format
     final List<String> inputParts = inputString.split('/');
     if (inputParts.length != 3) {
       return null;
     }
 
-    final int year = int.tryParse(inputParts[2], radix: 10);
+    final int? year = int.tryParse(inputParts[2], radix: 10);
     if (year == null || year < 1) {
       return null;
     }
 
-    final int month = int.tryParse(inputParts[0], radix: 10);
+    final int? month = int.tryParse(inputParts[0], radix: 10);
     if (month == null || month < 1 || month > 12) {
       return null;
     }
 
-    final int day = int.tryParse(inputParts[1], radix: 10);
+    final int? day = int.tryParse(inputParts[1], radix: 10);
     if (day == null || day < 1 || day > _getDaysInMonth(year, month)) {
       return null;
     }
@@ -808,7 +810,6 @@ class DefaultMaterialLocalizations implements MaterialLocalizations {
       case DayPeriod.pm:
         return postMeridiemAbbreviation;
     }
-    return null;
   }
 
   @override
@@ -932,7 +933,7 @@ class DefaultMaterialLocalizations implements MaterialLocalizations {
   String get rowsPerPageTitle => 'Rows per page:';
 
   @override
-  String tabLabel({ int tabIndex, int tabCount }) {
+  String tabLabel({ required int tabIndex, required int tabCount }) {
     assert(tabIndex >= 1);
     assert(tabCount >= 1);
     return 'Tab $tabIndex of $tabCount';

packages/flutter/lib/src/material/snack_bar_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';
@@ -67,30 +65,30 @@ class SnackBarThemeData with Diagnosticable {
   /// Default value for [SnackBar.backgroundColor].
   ///
   /// If null, [SnackBar] defaults to dark grey: `Color(0xFF323232)`.
-  final Color backgroundColor;
+  final Color? backgroundColor;
 
   /// Default value for [SnackBarAction.textColor].
   ///
   /// If null, [SnackBarAction] defaults to [ColorScheme.secondary] of
   /// [ThemeData.colorScheme] .
-  final Color actionTextColor;
+  final Color? actionTextColor;
 
   /// Default value for [SnackBarAction.disabledTextColor].
   ///
   /// If null, [SnackBarAction] defaults to [ColorScheme.onSurface] with its
   /// opacity set to 0.30 if the [Theme]'s brightness is [Brightness.dark], 0.38
   /// otherwise.
-  final Color disabledActionTextColor;
+  final Color? disabledActionTextColor;
 
   /// Used to configure the [DefaultTextStyle] for the [SnackBar.content] widget.
   ///
   /// If null, [SnackBar] defines its default.
-  final TextStyle contentTextStyle;
+  final TextStyle? contentTextStyle;
 
   /// Default value for [SnackBar.elevation].
   ///
   /// If null, [SnackBar] uses a default of 6.0.
-  final double elevation;
+  final double? elevation;
 
   /// Default value for [SnackBar.shape].
   ///
@@ -99,23 +97,23 @@ class SnackBarThemeData with Diagnosticable {
   /// specified, so the [SnackBar] is rectangular. For
   /// [SnackBarBehavior.floating], it uses a [RoundedRectangleBorder] with a
   /// circular corner radius of 4.0.
-  final ShapeBorder shape;
+  final ShapeBorder? shape;
 
   /// Default value for [SnackBar.behavior].
   ///
   /// If null, [SnackBar] will default to [SnackBarBehavior.fixed].
-  final SnackBarBehavior behavior;
+  final SnackBarBehavior? behavior;
 
   /// Creates a copy of this object with the given fields replaced with the
   /// new values.
   SnackBarThemeData copyWith({
-    Color backgroundColor,
-    Color actionTextColor,
-    Color disabledActionTextColor,
-    TextStyle contentTextStyle,
-    double elevation,
-    ShapeBorder shape,
-    SnackBarBehavior behavior,
+    Color? backgroundColor,
+    Color? actionTextColor,
+    Color? disabledActionTextColor,
+    TextStyle? contentTextStyle,
+    double? elevation,
+    ShapeBorder? shape,
+    SnackBarBehavior? behavior,
   }) {
     return SnackBarThemeData(
       backgroundColor: backgroundColor ?? this.backgroundColor,
@@ -133,7 +131,7 @@ class SnackBarThemeData with Diagnosticable {
   /// The argument `t` must not be null.
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static SnackBarThemeData lerp(SnackBarThemeData a, SnackBarThemeData b, double t) {
+  static SnackBarThemeData lerp(SnackBarThemeData? a, SnackBarThemeData? b, double t) {
     assert(t != null);
     return SnackBarThemeData(
       backgroundColor: Color.lerp(a?.backgroundColor, b?.backgroundColor, t),
@@ -142,7 +140,7 @@ class SnackBarThemeData with Diagnosticable {
       contentTextStyle: TextStyle.lerp(a?.contentTextStyle, b?.contentTextStyle, t),
       elevation: lerpDouble(a?.elevation, b?.elevation, t),
       shape: ShapeBorder.lerp(a?.shape, b?.shape, t),
-      behavior: t < 0.5 ? a.behavior : b.behavior,
+      behavior: t < 0.5 ? a?.behavior : b?.behavior,
     );
   }
 

packages/flutter/lib/src/material/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 'package:flutter/cupertino.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
@@ -40,10 +38,10 @@ class Theme extends StatelessWidget {
   ///
   /// The [data] and [child] arguments must not be null.
   const Theme({
-    Key key,
-    @required this.data,
+    Key? key,
+    required this.data,
     this.isMaterialAppTheme = false,
-    @required this.child,
+    required this.child,
   }) : assert(child != null),
        assert(data != null),
        super(key: key);
@@ -126,17 +124,17 @@ class Theme extends StatelessWidget {
   ///   );
   /// }
   /// ```
-  static ThemeData of(BuildContext context, { bool shadowThemeOnly = false }) {
-    final _InheritedTheme inheritedTheme = context.dependOnInheritedWidgetOfExactType<_InheritedTheme>();
+  static ThemeData? of(BuildContext context, { bool shadowThemeOnly = false }) {
+    final _InheritedTheme? inheritedTheme = context.dependOnInheritedWidgetOfExactType<_InheritedTheme>();
     if (shadowThemeOnly) {
       if (inheritedTheme == null || inheritedTheme.theme.isMaterialAppTheme)
         return null;
       return inheritedTheme.theme.data;
     }
 
-    final MaterialLocalizations localizations = MaterialLocalizations.of(context);
+    final MaterialLocalizations? localizations = MaterialLocalizations.of(context);
     final ScriptCategory category = localizations?.scriptCategory ?? ScriptCategory.englishLike;
-    final ThemeData theme = inheritedTheme?.theme?.data ?? _kFallbackTheme;
+    final ThemeData theme = inheritedTheme?.theme.data ?? _kFallbackTheme;
     return ThemeData.localize(theme, theme.typography.geometryThemeFor(category));
   }
 
@@ -168,9 +166,9 @@ class Theme extends StatelessWidget {
 
 class _InheritedTheme extends InheritedTheme {
   const _InheritedTheme({
-    Key key,
-    @required this.theme,
-    @required Widget child,
+    Key? key,
+    required this.theme,
+    required Widget child,
   }) : assert(theme != null),
        super(key: key, child: child);
 
@@ -178,7 +176,7 @@ class _InheritedTheme extends InheritedTheme {
 
   @override
   Widget wrap(BuildContext context, Widget child) {
-    final _InheritedTheme ancestorTheme = context.findAncestorWidgetOfExactType<_InheritedTheme>();
+    final _InheritedTheme? ancestorTheme = context.findAncestorWidgetOfExactType<_InheritedTheme>();
     return identical(this, ancestorTheme) ? child : Theme(data: theme.data, child: child);
   }
 
@@ -198,10 +196,10 @@ class ThemeDataTween extends Tween<ThemeData> {
   /// The [begin] and [end] properties must be non-null before the tween is
   /// first used, but the arguments can be null if the values are going to be
   /// filled in later.
-  ThemeDataTween({ ThemeData begin, ThemeData end }) : super(begin: begin, end: end);
+  ThemeDataTween({ ThemeData? begin, ThemeData? end }) : super(begin: begin, end: end);
 
   @override
-  ThemeData lerp(double t) => ThemeData.lerp(begin, end, t);
+  ThemeData lerp(double t) => ThemeData.lerp(begin!, end!, t);
 }
 
 /// Animated version of [Theme] which automatically transitions the colors,
@@ -224,13 +222,13 @@ class AnimatedTheme extends ImplicitlyAnimatedWidget {
   /// By default, the theme transition uses a linear curve. The [data] and
   /// [child] arguments must not be null.
   const AnimatedTheme({
-    Key key,
-    @required this.data,
+    Key? key,
+    required this.data,
     this.isMaterialAppTheme = false,
     Curve curve = Curves.linear,
     Duration duration = kThemeAnimationDuration,
-    VoidCallback onEnd,
-    @required this.child,
+    VoidCallback? onEnd,
+    required this.child,
   }) : assert(child != null),
        assert(data != null),
        super(key: key, curve: curve, duration: duration, onEnd: onEnd);
@@ -251,7 +249,7 @@ class AnimatedTheme extends ImplicitlyAnimatedWidget {
 }
 
 class _AnimatedThemeState extends AnimatedWidgetBaseState<AnimatedTheme> {
-  ThemeDataTween _data;
+  ThemeDataTween? _data;
 
   @override
   void forEachTween(TweenVisitor<dynamic> visitor) {
@@ -265,7 +263,7 @@ class _AnimatedThemeState extends AnimatedWidgetBaseState<AnimatedTheme> {
     return Theme(
       isMaterialAppTheme: widget.isMaterialAppTheme,
       child: widget.child,
-      data: _data.evaluate(animation),
+      data: _data!.evaluate(animation!),
     );
   }
 

packages/flutter/lib/src/material/time.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 hashValues;
 
 import 'package:flutter/widgets.dart';
@@ -53,7 +51,7 @@ class TimeOfDay {
   ///
   /// The [hour] argument must be between 0 and 23, inclusive. The [minute]
   /// argument must be between 0 and 59, inclusive.
-  const TimeOfDay({ @required this.hour, @required this.minute });
+  const TimeOfDay({ required this.hour, required this.minute });
 
   /// Creates a time of day based on the given time.
   ///
@@ -79,7 +77,7 @@ class TimeOfDay {
   static const int minutesPerHour = 60;
 
   /// Returns a new TimeOfDay with the hour and/or minute replaced.
-  TimeOfDay replacing({ int hour, int minute }) {
+  TimeOfDay replacing({ int? hour, int? minute }) {
     assert(hour == null || (hour >= 0 && hour < hoursPerDay));
     assert(minute == null || (minute >= 0 && minute < minutesPerHour));
     return TimeOfDay(hour: hour ?? this.hour, minute: minute ?? this.minute);
@@ -106,10 +104,10 @@ class TimeOfDay {
   String format(BuildContext context) {
     assert(debugCheckHasMediaQuery(context));
     assert(debugCheckHasMaterialLocalizations(context));
-    final MaterialLocalizations localizations = MaterialLocalizations.of(context);
+    final MaterialLocalizations localizations = MaterialLocalizations.of(context)!;
     return localizations.formatTimeOfDay(
       this,
-      alwaysUse24HourFormat: MediaQuery.of(context).alwaysUse24HourFormat,
+      alwaysUse24HourFormat: MediaQuery.of(context)!.alwaysUse24HourFormat,
     );
   }
 
@@ -204,7 +202,7 @@ enum HourFormat {
 }
 
 /// The [HourFormat] used for the given [TimeOfDayFormat].
-HourFormat hourFormat({ @required TimeOfDayFormat of }) {
+HourFormat hourFormat({ required TimeOfDayFormat of }) {
   switch (of) {
     case TimeOfDayFormat.h_colon_mm_space_a:
     case TimeOfDayFormat.a_space_h_colon_mm:
@@ -216,6 +214,4 @@ HourFormat hourFormat({ @required TimeOfDayFormat of }) {
     case TimeOfDayFormat.frenchCanadian:
       return HourFormat.HH;
   }
-
-  return null;
 }

packages/flutter/lib/src/material/tooltip_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';
@@ -42,13 +40,13 @@ class TooltipThemeData with Diagnosticable {
   });
 
   /// The height of [Tooltip.child].
-  final double height;
+  final double? height;
 
   /// If provided, the amount of space by which to inset [Tooltip.child].
-  final EdgeInsetsGeometry padding;
+  final EdgeInsetsGeometry? padding;
 
   /// If provided, the amount of empty space to surround the [Tooltip].
-  final EdgeInsetsGeometry margin;
+  final EdgeInsetsGeometry? margin;
 
   /// The vertical gap between the widget and the displayed tooltip.
   ///
@@ -57,13 +55,13 @@ class TooltipThemeData with Diagnosticable {
   /// tooltips will position themselves under their corresponding widgets.
   /// Otherwise, tooltips will position themselves above their corresponding
   /// widgets with the given offset.
-  final double verticalOffset;
+  final double? verticalOffset;
 
   /// Whether the tooltip is displayed below its widget by default.
   ///
   /// If there is insufficient space to display the tooltip in the preferred
   /// direction, the tooltip will be displayed in the opposite direction.
-  final bool preferBelow;
+  final bool? preferBelow;
 
   /// Whether the [Tooltip.message] should be excluded from the semantics
   /// tree.
@@ -71,34 +69,34 @@ class TooltipThemeData with Diagnosticable {
   /// By default, [Tooltip]s will add a [Semantics] label that is set to
   /// [Tooltip.message]. Set this property to true if the app is going to
   /// provide its own custom semantics label.
-  final bool excludeFromSemantics;
+  final bool? excludeFromSemantics;
 
   /// The [Tooltip]'s shape and background color.
-  final Decoration decoration;
+  final Decoration? decoration;
 
   /// The style to use for the message of [Tooltip]s.
-  final TextStyle textStyle;
+  final TextStyle? textStyle;
 
   /// The length of time that a pointer must hover over a tooltip's widget
   /// before the tooltip will be shown.
-  final Duration waitDuration;
+  final Duration? waitDuration;
 
   /// The length of time that the tooltip will be shown once it has appeared.
-  final Duration showDuration;
+  final Duration? showDuration;
 
   /// Creates a copy of this object but with the given fields replaced with the
   /// new values.
   TooltipThemeData copyWith({
-    double height,
-    EdgeInsetsGeometry padding,
-    EdgeInsetsGeometry margin,
-    double verticalOffset,
-    bool preferBelow,
-    bool excludeFromSemantics,
-    Decoration decoration,
-    TextStyle textStyle,
-    Duration waitDuration,
-    Duration showDuration,
+    double? height,
+    EdgeInsetsGeometry? padding,
+    EdgeInsetsGeometry? margin,
+    double? verticalOffset,
+    bool? preferBelow,
+    bool? excludeFromSemantics,
+    Decoration? decoration,
+    TextStyle? textStyle,
+    Duration? waitDuration,
+    Duration? showDuration,
   }) {
     return TooltipThemeData(
       height: height ?? this.height,
@@ -119,7 +117,7 @@ class TooltipThemeData with Diagnosticable {
   /// If both arguments are null, then null is returned.
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static TooltipThemeData lerp(TooltipThemeData a, TooltipThemeData b, double t) {
+  static TooltipThemeData? lerp(TooltipThemeData? a, TooltipThemeData? b, double t) {
     if (a == null && b == null)
       return null;
     assert(t != null);
@@ -128,8 +126,8 @@ class TooltipThemeData with Diagnosticable {
       padding: EdgeInsetsGeometry.lerp(a?.padding, b?.padding, t),
       margin: EdgeInsetsGeometry.lerp(a?.margin, b?.margin, t),
       verticalOffset: lerpDouble(a?.verticalOffset, b?.verticalOffset, t),
-      preferBelow: t < 0.5 ? a.preferBelow: b.preferBelow,
-      excludeFromSemantics: t < 0.5 ? a.excludeFromSemantics : b.excludeFromSemantics,
+      preferBelow: t < 0.5 ? a?.preferBelow: b?.preferBelow,
+      excludeFromSemantics: t < 0.5 ? a?.excludeFromSemantics : b?.excludeFromSemantics,
       decoration: Decoration.lerp(a?.decoration, b?.decoration, t),
       textStyle: TextStyle.lerp(a?.textStyle, b?.textStyle, t),
     );
@@ -222,9 +220,9 @@ class TooltipTheme extends InheritedTheme {
   ///
   /// The data argument must not be null.
   const TooltipTheme({
-    Key key,
-    @required this.data,
-    Widget child,
+    Key? key,
+    required this.data,
+    required Widget child,
   }) : assert(data != null), super(key: key, child: child);
 
   /// The properties for descendant [Tooltip] widgets.
@@ -240,13 +238,13 @@ class TooltipTheme extends InheritedTheme {
   /// TooltipThemeData theme = TooltipTheme.of(context);
   /// ```
   static TooltipThemeData of(BuildContext context) {
-    final TooltipTheme tooltipTheme = context.dependOnInheritedWidgetOfExactType<TooltipTheme>();
-    return tooltipTheme?.data ?? Theme.of(context).tooltipTheme;
+    final TooltipTheme? tooltipTheme = context.dependOnInheritedWidgetOfExactType<TooltipTheme>();
+    return tooltipTheme?.data ?? Theme.of(context)!.tooltipTheme;
   }
 
   @override
   Widget wrap(BuildContext context, Widget child) {
-    final TooltipTheme ancestorTheme = context.findAncestorWidgetOfExactType<TooltipTheme>();
+    final TooltipTheme? ancestorTheme = context.findAncestorWidgetOfExactType<TooltipTheme>();
     return identical(this, ancestorTheme) ? child : TooltipTheme(data: data, child: child);
   }