migrate part of painting to nullsafety (#62951)

packages/flutter/lib/src/painting/_network_image_io.dart

@@ -2,7 +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:async';
 import 'dart:io';
@@ -33,7 +32,7 @@ class NetworkImage extends image_provider.ImageProvider<image_provider.NetworkIm
   final double scale;
 
   @override
-  final Map<String, String> headers;
+  final Map<String, String>? headers;
 
   @override
   Future<NetworkImage> obtainKey(image_provider.ImageConfiguration configuration) {
@@ -71,7 +70,7 @@ class NetworkImage extends image_provider.ImageProvider<image_provider.NetworkIm
     HttpClient client = _sharedHttpClient;
     assert(() {
       if (debugNetworkImageHttpClientProvider != null)
-        client = debugNetworkImageHttpClientProvider();
+        client = debugNetworkImageHttpClientProvider!();
       return true;
     }());
     return client;
@@ -102,7 +101,7 @@ class NetworkImage extends image_provider.ImageProvider<image_provider.NetworkIm
 
       final Uint8List bytes = await consolidateHttpClientResponseBytes(
         response,
-        onBytesReceived: (int cumulative, int total) {
+        onBytesReceived: (int cumulative, int? total) {
           chunkEvents.add(ImageChunkEvent(
             cumulativeBytesLoaded: cumulative,
             expectedTotalBytes: total,
@@ -118,7 +117,7 @@ class NetworkImage extends image_provider.ImageProvider<image_provider.NetworkIm
       // have had a chance to track the key in the cache at all.
       // Schedule a microtask to give the cache a chance to add the key.
       scheduleMicrotask(() {
-        PaintingBinding.instance.imageCache.evict(key);
+        PaintingBinding.instance!.imageCache!.evict(key);
       });
       rethrow;
     } finally {

packages/flutter/lib/src/painting/_network_image_web.dart

@@ -2,7 +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:async';
 import 'dart:ui' as ui;
@@ -33,7 +32,7 @@ class NetworkImage
   final double scale;
 
   @override
-  final Map<String, String> headers;
+  final Map<String, String>? headers;
 
   @override
   Future<NetworkImage> obtainKey(
@@ -58,9 +57,9 @@ class NetworkImage
         informationCollector: _imageStreamInformationCollector(key));
   }
 
-  InformationCollector _imageStreamInformationCollector(
+  InformationCollector? _imageStreamInformationCollector(
       image_provider.NetworkImage key) {
-    InformationCollector collector;
+    InformationCollector? collector;
     assert(() {
       collector = () {
         return <DiagnosticsNode>[

packages/flutter/lib/src/painting/beveled_rectangle_border.dart

@@ -2,7 +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;
 
@@ -57,24 +56,24 @@ class BeveledRectangleBorder extends OutlinedBorder {
   }
 
   @override
-  ShapeBorder lerpFrom(ShapeBorder a, double t) {
+  ShapeBorder? lerpFrom(ShapeBorder? a, double t) {
     assert(t != null);
     if (a is BeveledRectangleBorder) {
       return BeveledRectangleBorder(
         side: BorderSide.lerp(a.side, side, t),
-        borderRadius: BorderRadiusGeometry.lerp(a.borderRadius, borderRadius, t),
+        borderRadius: BorderRadiusGeometry.lerp(a.borderRadius, borderRadius, t)!,
       );
     }
     return super.lerpFrom(a, t);
   }
 
   @override
-  ShapeBorder lerpTo(ShapeBorder b, double t) {
+  ShapeBorder? lerpTo(ShapeBorder? b, double t) {
     assert(t != null);
     if (b is BeveledRectangleBorder) {
       return BeveledRectangleBorder(
         side: BorderSide.lerp(side, b.side, t),
-        borderRadius: BorderRadiusGeometry.lerp(borderRadius, b.borderRadius, t),
+        borderRadius: BorderRadiusGeometry.lerp(borderRadius, b.borderRadius, t)!,
       );
     }
     return super.lerpTo(b, t);
@@ -83,7 +82,7 @@ class BeveledRectangleBorder extends OutlinedBorder {
   /// Returns a copy of this RoundedRectangleBorder with the given fields
   /// replaced with the new values.
   @override
-  BeveledRectangleBorder copyWith({ BorderSide side, BorderRadius borderRadius }) {
+  BeveledRectangleBorder copyWith({ BorderSide? side, BorderRadius? borderRadius }) {
     return BeveledRectangleBorder(
       side: side ?? this.side,
       borderRadius: borderRadius ?? this.borderRadius,
@@ -120,17 +119,17 @@ class BeveledRectangleBorder extends OutlinedBorder {
   }
 
   @override
-  Path getInnerPath(Rect rect, { TextDirection textDirection }) {
+  Path getInnerPath(Rect rect, { TextDirection? textDirection }) {
     return _getPath(borderRadius.resolve(textDirection).toRRect(rect).deflate(side.width));
   }
 
   @override
-  Path getOuterPath(Rect rect, { TextDirection textDirection }) {
+  Path getOuterPath(Rect rect, { TextDirection? textDirection }) {
     return _getPath(borderRadius.resolve(textDirection).toRRect(rect));
   }
 
   @override
-  void paint(Canvas canvas, Rect rect, { TextDirection textDirection }) {
+  void paint(Canvas canvas, Rect rect, { TextDirection? textDirection }) {
     if (rect.isEmpty)
       return;
     switch (side.style) {

packages/flutter/lib/src/painting/border_radius.dart

@@ -2,7 +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';
 
@@ -130,7 +129,7 @@ abstract class BorderRadiusGeometry {
   /// into a concrete [BorderRadius] using [resolve].
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static BorderRadiusGeometry lerp(BorderRadiusGeometry a, BorderRadiusGeometry b, double t) {
+  static BorderRadiusGeometry? lerp(BorderRadiusGeometry? a, BorderRadiusGeometry? b, double t) {
     assert(t != null);
     if (a == null && b == null)
       return null;
@@ -148,11 +147,11 @@ abstract class BorderRadiusGeometry {
   ///  * [BorderRadius], for which this is a no-op (returns itself).
   ///  * [BorderRadiusDirectional], which flips the horizontal direction
   ///    based on the `direction` argument.
-  BorderRadius resolve(TextDirection direction);
+  BorderRadius resolve(TextDirection? direction);
 
   @override
   String toString() {
-    String visual, logical;
+    String? visual, logical;
     if (_topLeft == _topRight &&
         _topRight == _bottomLeft &&
         _bottomLeft == _bottomRight) {
@@ -474,24 +473,24 @@ class BorderRadius extends BorderRadiusGeometry {
   /// If either is null, this function interpolates from [BorderRadius.zero].
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static BorderRadius lerp(BorderRadius a, BorderRadius b, double t) {
+  static BorderRadius? lerp(BorderRadius? a, BorderRadius? b, double t) {
     assert(t != null);
     if (a == null && b == null)
       return null;
     if (a == null)
-      return b * t;
+      return b! * t;
     if (b == null)
       return a * (1.0 - t);
     return BorderRadius.only(
-      topLeft: Radius.lerp(a.topLeft, b.topLeft, t),
-      topRight: Radius.lerp(a.topRight, b.topRight, t),
-      bottomLeft: Radius.lerp(a.bottomLeft, b.bottomLeft, t),
-      bottomRight: Radius.lerp(a.bottomRight, b.bottomRight, t),
+      topLeft: Radius.lerp(a.topLeft, b.topLeft, t)!,
+      topRight: Radius.lerp(a.topRight, b.topRight, t)!,
+      bottomLeft: Radius.lerp(a.bottomLeft, b.bottomLeft, t)!,
+      bottomRight: Radius.lerp(a.bottomRight, b.bottomRight, t)!,
     );
   }
 
   @override
-  BorderRadius resolve(TextDirection direction) => this;
+  BorderRadius resolve(TextDirection? direction) => this;
 }
 
 /// An immutable set of radii for each corner of a rectangle, but with the
@@ -691,26 +690,26 @@ class BorderRadiusDirectional extends BorderRadiusGeometry {
   /// If either is null, this function interpolates from [BorderRadiusDirectional.zero].
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static BorderRadiusDirectional lerp(BorderRadiusDirectional a, BorderRadiusDirectional b, double t) {
+  static BorderRadiusDirectional? lerp(BorderRadiusDirectional? a, BorderRadiusDirectional? b, double t) {
     assert(t != null);
     if (a == null && b == null)
       return null;
     if (a == null)
-      return b * t;
+      return b! * t;
     if (b == null)
       return a * (1.0 - t);
     return BorderRadiusDirectional.only(
-      topStart: Radius.lerp(a.topStart, b.topStart, t),
-      topEnd: Radius.lerp(a.topEnd, b.topEnd, t),
-      bottomStart: Radius.lerp(a.bottomStart, b.bottomStart, t),
-      bottomEnd: Radius.lerp(a.bottomEnd, b.bottomEnd, t),
+      topStart: Radius.lerp(a.topStart, b.topStart, t)!,
+      topEnd: Radius.lerp(a.topEnd, b.topEnd, t)!,
+      bottomStart: Radius.lerp(a.bottomStart, b.bottomStart, t)!,
+      bottomEnd: Radius.lerp(a.bottomEnd, b.bottomEnd, t)!,
     );
   }
 
   @override
-  BorderRadius resolve(TextDirection direction) {
+  BorderRadius resolve(TextDirection? direction) {
     assert(direction != null);
-    switch (direction) {
+    switch (direction!) {
       case TextDirection.rtl:
         return BorderRadius.only(
           topLeft: topEnd,
@@ -726,7 +725,6 @@ class BorderRadiusDirectional extends BorderRadiusGeometry {
           bottomRight: bottomEnd,
         );
     }
-    return null;
   }
 }
 
@@ -838,9 +836,9 @@ class _MixedBorderRadius extends BorderRadiusGeometry {
   }
 
   @override
-  BorderRadius resolve(TextDirection direction) {
+  BorderRadius resolve(TextDirection? direction) {
     assert(direction != null);
-    switch (direction) {
+    switch (direction!) {
       case TextDirection.rtl:
         return BorderRadius.only(
           topLeft: _topLeft + _topEnd,
@@ -856,6 +854,5 @@ class _MixedBorderRadius extends BorderRadiusGeometry {
           bottomRight: _bottomRight + _bottomEnd,
         );
     }
-    return null;
   }
 }

packages/flutter/lib/src/painting/borders.dart

@@ -2,7 +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 'dart:ui' as ui show lerpDouble;
@@ -130,9 +129,9 @@ class BorderSide {
 
   /// Creates a copy of this border but with the given fields replaced with the new values.
   BorderSide copyWith({
-    Color color,
-    double width,
-    BorderStyle style,
+    Color? color,
+    double? width,
+    BorderStyle? style,
   }) {
     assert(width == null || width >= 0.0);
     return BorderSide(
@@ -186,7 +185,6 @@ class BorderSide {
           ..strokeWidth = 0.0
           ..style = PaintingStyle.stroke;
     }
-    return null;
   }
 
   /// Whether the two given [BorderSide]s can be merged using [new
@@ -219,12 +217,12 @@ class BorderSide {
       return a;
     if (t == 1.0)
       return b;
-    final double width = ui.lerpDouble(a.width, b.width, t);
+    final double width = ui.lerpDouble(a.width, b.width, t)!;
     if (width < 0.0)
       return BorderSide.none;
     if (a.style == b.style) {
       return BorderSide(
-        color: Color.lerp(a.color, b.color, t),
+        color: Color.lerp(a.color, b.color, t)!,
         width: width,
         style: a.style, // == b.style
       );
@@ -247,7 +245,7 @@ class BorderSide {
         break;
     }
     return BorderSide(
-      color: Color.lerp(colorA, colorB, t),
+      color: Color.lerp(colorA, colorB, t)!,
       width: width,
       style: BorderStyle.solid,
     );
@@ -319,7 +317,7 @@ abstract class ShapeBorder {
   /// The `reversed` argument is true if this object was the right operand of
   /// the `+` operator, and false if it was the left operand.
   @protected
-  ShapeBorder add(ShapeBorder other, { bool reversed = false }) => null;
+  ShapeBorder? add(ShapeBorder other, { bool reversed = false }) => null;
 
   /// Creates a new border consisting of the two borders on either side of the
   /// operator.
@@ -382,7 +380,7 @@ abstract class ShapeBorder {
   ///
   /// Instead of calling this directly, use [ShapeBorder.lerp].
   @protected
-  ShapeBorder lerpFrom(ShapeBorder a, double t) {
+  ShapeBorder? lerpFrom(ShapeBorder? a, double t) {
     if (a == null)
       return scale(t);
     return null;
@@ -414,7 +412,7 @@ abstract class ShapeBorder {
   ///
   /// Instead of calling this directly, use [ShapeBorder.lerp].
   @protected
-  ShapeBorder lerpTo(ShapeBorder b, double t) {
+  ShapeBorder? lerpTo(ShapeBorder? b, double t) {
     if (b == null)
       return scale(1.0 - t);
     return null;
@@ -428,9 +426,9 @@ abstract class ShapeBorder {
   /// and `b` after `t=0.5`.
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static ShapeBorder lerp(ShapeBorder a, ShapeBorder b, double t) {
+  static ShapeBorder? lerp(ShapeBorder? a, ShapeBorder? b, double t) {
     assert(t != null);
-    ShapeBorder result;
+    ShapeBorder? result;
     if (b != null)
       result = b.lerpFrom(a, t);
     if (result == null && a != null)
@@ -457,7 +455,7 @@ abstract class ShapeBorder {
   ///
   ///  * [getInnerPath], which creates the path for the inner edge.
   ///  * [Path.contains], which can tell if an [Offset] is within a [Path].
-  Path getOuterPath(Rect rect, { TextDirection textDirection });
+  Path getOuterPath(Rect rect, { TextDirection? textDirection });
 
   /// Create a [Path] that describes the inner edge of the border.
   ///
@@ -478,7 +476,7 @@ abstract class ShapeBorder {
   ///
   ///  * [getOuterPath], which creates the path for the outer edge.
   ///  * [Path.contains], which can tell if an [Offset] is within a [Path].
-  Path getInnerPath(Rect rect, { TextDirection textDirection });
+  Path getInnerPath(Rect rect, { TextDirection? textDirection });
 
   /// Paints the border within the given [Rect] on the given [Canvas].
   ///
@@ -486,7 +484,7 @@ abstract class ShapeBorder {
   /// has a text direction dependency (for example if it is expressed in terms
   /// of "start" and "end" instead of "left" and "right"). It may be null if
   /// the border will not need the text direction to paint itself.
-  void paint(Canvas canvas, Rect rect, { TextDirection textDirection });
+  void paint(Canvas canvas, Rect rect, { TextDirection? textDirection });
 
   @override
   String toString() {
@@ -548,7 +546,7 @@ class _CompoundBorder extends ShapeBorder {
       // border, and "merged" is the result of attempting to merge it with the
       // new border. If it's null, it couldn't be merged.
       final ShapeBorder ours = reversed ? borders.last : borders.first;
-      final ShapeBorder merged = ours.add(other, reversed: reversed)
+      final ShapeBorder? merged = ours.add(other, reversed: reversed)
                              ?? other.add(ours, reversed: !reversed);
       if (merged != null) {
         final List<ShapeBorder> result = <ShapeBorder>[...borders];
@@ -574,27 +572,27 @@ class _CompoundBorder extends ShapeBorder {
   }
 
   @override
-  ShapeBorder lerpFrom(ShapeBorder a, double t) {
+  ShapeBorder? lerpFrom(ShapeBorder? a, double t) {
     return _CompoundBorder.lerp(a, this, t);
   }
 
   @override
-  ShapeBorder lerpTo(ShapeBorder b, double t) {
+  ShapeBorder? lerpTo(ShapeBorder? b, double t) {
     return _CompoundBorder.lerp(this, b, t);
   }
 
-  static _CompoundBorder lerp(ShapeBorder a, ShapeBorder b, double t) {
+  static _CompoundBorder lerp(ShapeBorder? a, ShapeBorder? b, double t) {
     assert(t != null);
     assert(a is _CompoundBorder || b is _CompoundBorder); // Not really necessary, but all call sites currently intend this.
-    final List<ShapeBorder> aList = a is _CompoundBorder ? a.borders : <ShapeBorder>[a];
-    final List<ShapeBorder> bList = b is _CompoundBorder ? b.borders : <ShapeBorder>[b];
+    final List<ShapeBorder?> aList = a is _CompoundBorder ? a.borders : <ShapeBorder?>[a];
+    final List<ShapeBorder?> bList = b is _CompoundBorder ? b.borders : <ShapeBorder?>[b];
     final List<ShapeBorder> results = <ShapeBorder>[];
     final int length = math.max(aList.length, bList.length);
     for (int index = 0; index < length; index += 1) {
-      final ShapeBorder localA = index < aList.length ? aList[index] : null;
-      final ShapeBorder localB = index < bList.length ? bList[index] : null;
+      final ShapeBorder? localA = index < aList.length ? aList[index] : null;
+      final ShapeBorder? localB = index < bList.length ? bList[index] : null;
       if (localA != null && localB != null) {
-        final ShapeBorder localResult = localA.lerpTo(localB, t) ?? localB.lerpFrom(localA, t);
+        final ShapeBorder? localResult = localA.lerpTo(localB, t) ?? localB.lerpFrom(localA, t);
         if (localResult != null) {
           results.add(localResult);
           continue;
@@ -613,19 +611,19 @@ class _CompoundBorder extends ShapeBorder {
   }
 
   @override
-  Path getInnerPath(Rect rect, { TextDirection textDirection }) {
+  Path getInnerPath(Rect rect, { TextDirection? textDirection }) {
     for (int index = 0; index < borders.length - 1; index += 1)
       rect = borders[index].dimensions.resolve(textDirection).deflateRect(rect);
     return borders.last.getInnerPath(rect, textDirection: textDirection);
   }
 
   @override
-  Path getOuterPath(Rect rect, { TextDirection textDirection }) {
+  Path getOuterPath(Rect rect, { TextDirection? textDirection }) {
     return borders.first.getOuterPath(rect, textDirection: textDirection);
   }
 
   @override
-  void paint(Canvas canvas, Rect rect, { TextDirection textDirection }) {
+  void paint(Canvas canvas, Rect rect, { TextDirection? textDirection }) {
     for (final ShapeBorder border in borders) {
       border.paint(canvas, rect, textDirection: textDirection);
       rect = border.dimensions.resolve(textDirection).deflateRect(rect);

packages/flutter/lib/src/painting/box_border.dart

@@ -2,7 +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';
 
@@ -85,7 +84,7 @@ abstract class BoxBorder extends ShapeBorder {
   // We override this to tighten the return value, so that callers can assume
   // that we'll return a [BoxBorder].
   @override
-  BoxBorder add(ShapeBorder other, { bool reversed = false }) => null;
+  BoxBorder? add(ShapeBorder other, { bool reversed = false }) => null;
 
   /// Linearly interpolate between two borders.
   ///
@@ -104,12 +103,12 @@ abstract class BoxBorder extends ShapeBorder {
   /// instead [add] the two sets of sides and interpolate them simultaneously.
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static BoxBorder lerp(BoxBorder a, BoxBorder b, double t) {
+  static BoxBorder? lerp(BoxBorder? a, BoxBorder? b, double t) {
     assert(t != null);
-    if ((a is Border || a == null) && (b is Border || b == null))
-      return Border.lerp(a as Border, b as Border, t);
-    if ((a is BorderDirectional || a == null) && (b is BorderDirectional || b == null))
-      return BorderDirectional.lerp(a as BorderDirectional, b as BorderDirectional, t);
+    if ((a is Border?) && (b is Border?))
+      return Border.lerp(a, b, t);
+    if ((a is BorderDirectional?) && (b is BorderDirectional?))
+      return BorderDirectional.lerp(a, b, t);
     if (b is Border && a is BorderDirectional) {
       final BoxBorder c = b;
       b = a;
@@ -167,14 +166,14 @@ abstract class BoxBorder extends ShapeBorder {
   }
 
   @override
-  Path getInnerPath(Rect rect, { @required TextDirection textDirection }) {
+  Path getInnerPath(Rect rect, { TextDirection? textDirection }) {
     assert(textDirection != null, 'The textDirection argument to $runtimeType.getInnerPath must not be null.');
     return Path()
       ..addRect(dimensions.resolve(textDirection).deflateRect(rect));
   }
 
   @override
-  Path getOuterPath(Rect rect, { @required TextDirection textDirection }) {
+  Path getOuterPath(Rect rect, { TextDirection? textDirection }) {
     assert(textDirection != null, 'The textDirection argument to $runtimeType.getOuterPath must not be null.');
     return Path()
       ..addRect(rect);
@@ -203,9 +202,9 @@ abstract class BoxBorder extends ShapeBorder {
   void paint(
     Canvas canvas,
     Rect rect, {
-    TextDirection textDirection,
+    TextDirection? textDirection,
     BoxShape shape = BoxShape.rectangle,
-    BorderRadius borderRadius,
+    BorderRadius? borderRadius,
   });
 
   static void _paintUniformBorderWithRadius(Canvas canvas, Rect rect, BorderSide side, BorderRadius borderRadius) {
@@ -414,7 +413,7 @@ class Border extends BoxBorder {
   }
 
   @override
-  Border add(ShapeBorder other, { bool reversed = false }) {
+  Border? add(ShapeBorder other, { bool reversed = false }) {
     if (other is Border &&
         BorderSide.canMerge(top, other.top) &&
         BorderSide.canMerge(right, other.right) &&
@@ -436,14 +435,14 @@ class Border extends BoxBorder {
   }
 
   @override
-  ShapeBorder lerpFrom(ShapeBorder a, double t) {
+  ShapeBorder? lerpFrom(ShapeBorder? a, double t) {
     if (a is Border)
       return Border.lerp(a, this, t);
     return super.lerpFrom(a, t);
   }
 
   @override
-  ShapeBorder lerpTo(ShapeBorder b, double t) {
+  ShapeBorder? lerpTo(ShapeBorder? b, double t) {
     if (b is Border)
       return Border.lerp(this, b, t);
     return super.lerpTo(b, t);
@@ -455,12 +454,12 @@ class Border extends BoxBorder {
   /// borders.
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static Border lerp(Border a, Border b, double t) {
+  static Border? lerp(Border? a, Border? b, double t) {
     assert(t != null);
     if (a == null && b == null)
       return null;
     if (a == null)
-      return b.scale(t);
+      return b!.scale(t);
     if (b == null)
       return a.scale(1.0 - t);
     return Border(
@@ -494,9 +493,9 @@ class Border extends BoxBorder {
   void paint(
     Canvas canvas,
     Rect rect, {
-    TextDirection textDirection,
+    TextDirection? textDirection,
     BoxShape shape = BoxShape.rectangle,
-    BorderRadius borderRadius,
+    BorderRadius? borderRadius,
   }) {
     if (isUniform) {
       switch (top.style) {
@@ -694,7 +693,7 @@ class BorderDirectional extends BoxBorder {
   }
 
   @override
-  BoxBorder add(ShapeBorder other, { bool reversed = false }) {
+  BoxBorder? add(ShapeBorder other, { bool reversed = false }) {
     if (other is BorderDirectional) {
       final BorderDirectional typedOther = other;
       if (BorderSide.canMerge(top, typedOther.top) &&
@@ -747,14 +746,14 @@ class BorderDirectional extends BoxBorder {
   }
 
   @override
-  ShapeBorder lerpFrom(ShapeBorder a, double t) {
+  ShapeBorder? lerpFrom(ShapeBorder? a, double t) {
     if (a is BorderDirectional)
       return BorderDirectional.lerp(a, this, t);
     return super.lerpFrom(a, t);
   }
 
   @override
-  ShapeBorder lerpTo(ShapeBorder b, double t) {
+  ShapeBorder? lerpTo(ShapeBorder? b, double t) {
     if (b is BorderDirectional)
       return BorderDirectional.lerp(this, b, t);
     return super.lerpTo(b, t);
@@ -766,12 +765,12 @@ class BorderDirectional extends BoxBorder {
   /// borders.
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static BorderDirectional lerp(BorderDirectional a, BorderDirectional b, double t) {
+  static BorderDirectional? lerp(BorderDirectional? a, BorderDirectional? b, double t) {
     assert(t != null);
     if (a == null && b == null)
       return null;
     if (a == null)
-      return b.scale(t);
+      return b!.scale(t);
     if (b == null)
       return a.scale(1.0 - t);
     return BorderDirectional(
@@ -808,9 +807,9 @@ class BorderDirectional extends BoxBorder {
   void paint(
     Canvas canvas,
     Rect rect, {
-    TextDirection textDirection,
+    TextDirection? textDirection,
     BoxShape shape = BoxShape.rectangle,
-    BorderRadius borderRadius,
+    BorderRadius? borderRadius,
   }) {
     if (isUniform) {
       switch (top.style) {
@@ -839,7 +838,7 @@ class BorderDirectional extends BoxBorder {
 
     BorderSide left, right;
     assert(textDirection != null, 'Non-uniform BorderDirectional objects require a TextDirection when painting.');
-    switch (textDirection) {
+    switch (textDirection!) {
       case TextDirection.rtl:
         left = end;
         right = start;

packages/flutter/lib/src/painting/box_fit.dart

@@ -2,7 +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;
 

packages/flutter/lib/src/painting/box_shadow.dart

@@ -2,7 +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 'dart:ui' as ui show Shadow, lerpDouble;
@@ -79,19 +78,19 @@ class BoxShadow extends ui.Shadow {
   /// offset and a zero blurRadius.
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static BoxShadow lerp(BoxShadow a, BoxShadow b, double t) {
+  static BoxShadow? lerp(BoxShadow? a, BoxShadow? b, double t) {
     assert(t != null);
     if (a == null && b == null)
       return null;
     if (a == null)
-      return b.scale(t);
+      return b!.scale(t);
     if (b == null)
       return a.scale(1.0 - t);
     return BoxShadow(
-      color: Color.lerp(a.color, b.color, t),
-      offset: Offset.lerp(a.offset, b.offset, t),
-      blurRadius: ui.lerpDouble(a.blurRadius, b.blurRadius, t),
-      spreadRadius: ui.lerpDouble(a.spreadRadius, b.spreadRadius, t),
+      color: Color.lerp(a.color, b.color, t)!,
+      offset: Offset.lerp(a.offset, b.offset, t)!,
+      blurRadius: ui.lerpDouble(a.blurRadius, b.blurRadius, t)!,
+      spreadRadius: ui.lerpDouble(a.spreadRadius, b.spreadRadius, t)!,
     );
   }
 
@@ -100,7 +99,7 @@ class BoxShadow extends ui.Shadow {
   /// If the lists differ in length, excess items are lerped with null.
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static List<BoxShadow> lerpList(List<BoxShadow> a, List<BoxShadow> b, double t) {
+  static List<BoxShadow>? lerpList(List<BoxShadow>? a, List<BoxShadow>? b, double t) {
     assert(t != null);
     if (a == null && b == null)
       return null;
@@ -108,7 +107,7 @@ class BoxShadow extends ui.Shadow {
     b ??= <BoxShadow>[];
     final int commonLength = math.min(a.length, b.length);
     return <BoxShadow>[
-      for (int i = 0; i < commonLength; i += 1) BoxShadow.lerp(a[i], b[i], t),
+      for (int i = 0; i < commonLength; i += 1) BoxShadow.lerp(a[i], b[i], t)!,
       for (int i = commonLength; i < a.length; i += 1) a[i].scale(1.0 - t),
       for (int i = commonLength; i < b.length; i += 1) b[i].scale(t),
     ];

packages/flutter/lib/src/painting/edge_insets.dart

@@ -2,7 +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' as ui show lerpDouble, WindowPadding;
 
@@ -73,7 +72,6 @@ abstract class EdgeInsetsGeometry {
       case Axis.vertical:
         return vertical;
     }
-    return null;
   }
 
   /// The size that this [EdgeInsets] would occupy with an empty interior.
@@ -218,12 +216,12 @@ abstract class EdgeInsetsGeometry {
   /// into a concrete [EdgeInsets] using [resolve].
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static EdgeInsetsGeometry lerp(EdgeInsetsGeometry a, EdgeInsetsGeometry b, double t) {
+  static EdgeInsetsGeometry? lerp(EdgeInsetsGeometry? a, EdgeInsetsGeometry? b, double t) {
     assert(t != null);
     if (a == null && b == null)
       return null;
     if (a == null)
-      return b * t;
+      return b! * t;
     if (b == null)
       return a * (1.0 - t);
     if (a is EdgeInsets && b is EdgeInsets)
@@ -231,12 +229,12 @@ abstract class EdgeInsetsGeometry {
     if (a is EdgeInsetsDirectional && b is EdgeInsetsDirectional)
       return EdgeInsetsDirectional.lerp(a, b, t);
     return _MixedEdgeInsets.fromLRSETB(
-      ui.lerpDouble(a._left, b._left, t),
-      ui.lerpDouble(a._right, b._right, t),
-      ui.lerpDouble(a._start, b._start, t),
-      ui.lerpDouble(a._end, b._end, t),
-      ui.lerpDouble(a._top, b._top, t),
-      ui.lerpDouble(a._bottom, b._bottom, t),
+      ui.lerpDouble(a._left, b._left, t)!,
+      ui.lerpDouble(a._right, b._right, t)!,
+      ui.lerpDouble(a._start, b._start, t)!,
+      ui.lerpDouble(a._end, b._end, t)!,
+      ui.lerpDouble(a._top, b._top, t)!,
+      ui.lerpDouble(a._bottom, b._bottom, t)!,
     );
   }
 
@@ -249,7 +247,7 @@ abstract class EdgeInsetsGeometry {
   ///  * [EdgeInsets], for which this is a no-op (returns itself).
   ///  * [EdgeInsetsDirectional], which flips the horizontal direction
   ///    based on the `direction` argument.
-  EdgeInsets resolve(TextDirection direction);
+  EdgeInsets resolve(TextDirection? direction);
 
   @override
   String toString() {
@@ -597,32 +595,32 @@ class EdgeInsets extends EdgeInsetsGeometry {
   /// If either is null, this function interpolates from [EdgeInsets.zero].
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static EdgeInsets lerp(EdgeInsets a, EdgeInsets b, double t) {
+  static EdgeInsets? lerp(EdgeInsets? a, EdgeInsets? b, double t) {
     assert(t != null);
     if (a == null && b == null)
       return null;
     if (a == null)
-      return b * t;
+      return b! * t;
     if (b == null)
       return a * (1.0 - t);
     return EdgeInsets.fromLTRB(
-      ui.lerpDouble(a.left, b.left, t),
-      ui.lerpDouble(a.top, b.top, t),
-      ui.lerpDouble(a.right, b.right, t),
-      ui.lerpDouble(a.bottom, b.bottom, t),
+      ui.lerpDouble(a.left, b.left, t)!,
+      ui.lerpDouble(a.top, b.top, t)!,
+      ui.lerpDouble(a.right, b.right, t)!,
+      ui.lerpDouble(a.bottom, b.bottom, t)!,
     );
   }
 
   @override
-  EdgeInsets resolve(TextDirection direction) => this;
+  EdgeInsets resolve(TextDirection? direction) => this;
 
   /// Creates a copy of this EdgeInsets but with the given fields replaced
   /// with the new values.
   EdgeInsets copyWith({
-    double left,
-    double top,
-    double right,
-    double bottom,
+    double? left,
+    double? top,
+    double? right,
+    double? bottom,
   }) {
     return EdgeInsets.only(
       left: left ?? this.left,
@@ -822,32 +820,31 @@ class EdgeInsetsDirectional extends EdgeInsetsGeometry {
   /// [EdgeInsetsGeometry.lerp] static method.
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static EdgeInsetsDirectional lerp(EdgeInsetsDirectional a, EdgeInsetsDirectional b, double t) {
+  static EdgeInsetsDirectional? lerp(EdgeInsetsDirectional? a, EdgeInsetsDirectional? b, double t) {
     assert(t != null);
     if (a == null && b == null)
       return null;
     if (a == null)
-      return b * t;
+      return b! * t;
     if (b == null)
       return a * (1.0 - t);
     return EdgeInsetsDirectional.fromSTEB(
-      ui.lerpDouble(a.start, b.start, t),
-      ui.lerpDouble(a.top, b.top, t),
-      ui.lerpDouble(a.end, b.end, t),
-      ui.lerpDouble(a.bottom, b.bottom, t),
+      ui.lerpDouble(a.start, b.start, t)!,
+      ui.lerpDouble(a.top, b.top, t)!,
+      ui.lerpDouble(a.end, b.end, t)!,
+      ui.lerpDouble(a.bottom, b.bottom, t)!,
     );
   }
 
   @override
-  EdgeInsets resolve(TextDirection direction) {
+  EdgeInsets resolve(TextDirection? direction) {
     assert(direction != null);
-    switch (direction) {
+    switch (direction!) {
       case TextDirection.rtl:
         return EdgeInsets.fromLTRB(end, top, start, bottom);
       case TextDirection.ltr:
         return EdgeInsets.fromLTRB(start, top, end, bottom);
     }
-    return null;
   }
 }
 
@@ -943,14 +940,13 @@ class _MixedEdgeInsets extends EdgeInsetsGeometry {
   }
 
   @override
-  EdgeInsets resolve(TextDirection direction) {
+  EdgeInsets resolve(TextDirection? direction) {
     assert(direction != null);
-    switch (direction) {
+    switch (direction!) {
       case TextDirection.rtl:
         return EdgeInsets.fromLTRB(_end + _left, _top, _start + _right, _bottom);
       case TextDirection.ltr:
         return EdgeInsets.fromLTRB(_start + _left, _top, _end + _right, _bottom);
     }
-    return null;
   }
 }

packages/flutter/lib/src/painting/image_provider.dart

@@ -2,7 +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:async';
 import 'dart:io';
@@ -23,7 +22,7 @@ import 'image_stream.dart';
 typedef _KeyAndErrorHandlerCallback<T> = void Function(T key, ImageErrorListener handleError);
 
 /// Signature used for error handling by [_createErrorHandlerAndKey].
-typedef _AsyncKeyErrorHandler<T> = Future<void> Function(T key, dynamic exception, StackTrace stack);
+typedef _AsyncKeyErrorHandler<T> = Future<void> Function(T key, dynamic exception, StackTrace? stack);
 
 /// Configuration information passed to the [ImageProvider.resolve] method to
 /// select a specific image.
@@ -54,12 +53,12 @@ class ImageConfiguration {
   /// All the arguments are optional. Configuration information is merely
   /// advisory and best-effort.
   ImageConfiguration copyWith({
-    AssetBundle bundle,
-    double devicePixelRatio,
-    Locale locale,
-    TextDirection textDirection,
-    Size size,
-    TargetPlatform platform,
+    AssetBundle? bundle,
+    double? devicePixelRatio,
+    Locale? locale,
+    TextDirection? textDirection,
+    Size? size,
+    TargetPlatform? platform,
   }) {
     return ImageConfiguration(
       bundle: bundle ?? this.bundle,
@@ -73,25 +72,25 @@ class ImageConfiguration {
 
   /// The preferred [AssetBundle] to use if the [ImageProvider] needs one and
   /// does not have one already selected.
-  final AssetBundle bundle;
+  final AssetBundle? bundle;
 
   /// The device pixel ratio where the image will be shown.
-  final double devicePixelRatio;
+  final double? devicePixelRatio;
 
   /// The language and region for which to select the image.
-  final Locale locale;
+  final Locale? locale;
 
   /// The reading direction of the language for which to select the image.
-  final TextDirection textDirection;
+  final TextDirection? textDirection;
 
   /// The size at which the image will be rendered.
-  final Size size;
+  final Size? size;
 
   /// The [TargetPlatform] for which assets should be used. This allows images
   /// to be specified in a platform-neutral fashion yet use different assets on
   /// different platforms, to match local conventions e.g. for color matching or
   /// shadows.
-  final TargetPlatform platform;
+  final TargetPlatform? platform;
 
   /// An image configuration that provides no additional information.
   ///
@@ -128,7 +127,7 @@ class ImageConfiguration {
     if (devicePixelRatio != null) {
       if (hasArguments)
         result.write(', ');
-      result.write('devicePixelRatio: ${devicePixelRatio.toStringAsFixed(1)}');
+      result.write('devicePixelRatio: ${devicePixelRatio!.toStringAsFixed(1)}');
       hasArguments = true;
     }
     if (locale != null) {
@@ -152,7 +151,7 @@ class ImageConfiguration {
     if (platform != null) {
       if (hasArguments)
         result.write(', ');
-      result.write('platform: ${describeEnum(platform)}');
+      result.write('platform: ${describeEnum(platform!)}');
       hasArguments = true;
     }
     result.write(')');
@@ -170,7 +169,7 @@ class ImageConfiguration {
 ///
 ///  * [ResizeImage], which uses this to override the `cacheWidth`,
 ///    `cacheHeight`, and `allowUpscaling` parameters.
-typedef DecoderCallback = Future<ui.Codec> Function(Uint8List bytes, {int cacheWidth, int cacheHeight, bool allowUpscaling});
+typedef DecoderCallback = Future<ui.Codec> Function(Uint8List bytes, {int? cacheWidth, int? cacheHeight, bool allowUpscaling});
 
 /// Identifies an image without committing to the precise final asset. This
 /// allows a set of images to be identified and for the precise image to later
@@ -306,7 +305,7 @@ typedef DecoderCallback = Future<ui.Codec> Function(Uint8List bytes, {int cacheW
 /// ```
 /// {@end-tool}
 @optionalTypeArgs
-abstract class ImageProvider<T> {
+abstract class ImageProvider<T extends Object> {
   /// Abstract const constructor. This constructor enables subclasses to provide
   /// const constructors so that they can be used in const expressions.
   const ImageProvider();
@@ -333,11 +332,11 @@ abstract class ImageProvider<T> {
       (T key, ImageErrorListener errorHandler) {
         resolveStreamForKey(configuration, stream, key, errorHandler);
       },
-      (T key, dynamic exception, StackTrace stack) async {
+      (T? key, dynamic exception, StackTrace? stack) async {
         await null; // wait an event turn in case a listener has been added to the image stream.
         final _ErrorImageCompleter imageCompleter = _ErrorImageCompleter();
         stream.setCompleter(imageCompleter);
-        InformationCollector collector;
+        InformationCollector? collector;
         assert(() {
           collector = () sync* {
             yield DiagnosticsProperty<ImageProvider>('Image provider', this);
@@ -379,21 +378,21 @@ abstract class ImageProvider<T> {
   ///
   /// A completed return value of null indicates that an error has occurred.
   Future<ImageCacheStatus> obtainCacheStatus({
-    @required ImageConfiguration configuration,
-    ImageErrorListener handleError,
+    required ImageConfiguration configuration,
+    ImageErrorListener? handleError,
   }) {
     assert(configuration != null);
     final Completer<ImageCacheStatus> completer = Completer<ImageCacheStatus>();
     _createErrorHandlerAndKey(
       configuration,
       (T key, ImageErrorListener innerHandleError) {
-        completer.complete(PaintingBinding.instance.imageCache.statusForKey(key));
+        completer.complete(PaintingBinding.instance!.imageCache!.statusForKey(key));
       },
-      (T key, dynamic exception, StackTrace stack) async {
+      (T? key, dynamic exception, StackTrace? stack) async {
         if (handleError != null) {
           handleError(exception, stack);
         } else {
-          InformationCollector collector;
+          InformationCollector? collector;
           assert(() {
             collector = () sync* {
               yield DiagnosticsProperty<ImageProvider>('Image provider', this);
@@ -402,12 +401,14 @@ abstract class ImageProvider<T> {
             };
             return true;
           }());
-          FlutterError.onError(FlutterErrorDetails(
-            context: ErrorDescription('while checking the cache location of an image'),
-            informationCollector: collector,
-            exception: exception,
-            stack: stack,
-          ));
+          if (FlutterError.onError != null) {
+            FlutterError.onError!(FlutterErrorDetails(
+              context: ErrorDescription('while checking the cache location of an image'),
+              informationCollector: collector,
+              exception: exception,
+              stack: stack,
+            ));
+          }
           completer.complete(null);
         }
       },
@@ -421,11 +422,11 @@ abstract class ImageProvider<T> {
   void _createErrorHandlerAndKey(
     ImageConfiguration configuration,
     _KeyAndErrorHandlerCallback<T> successCallback,
-    _AsyncKeyErrorHandler<T> errorCallback,
+    _AsyncKeyErrorHandler<T?> errorCallback,
   ) {
-    T obtainedKey;
+    T? obtainedKey;
     bool didError = false;
-    Future<void> handleError(dynamic exception, StackTrace stack) async {
+    Future<void> handleError(dynamic exception, StackTrace? stack) async {
       if (didError) {
         return;
       }
@@ -492,17 +493,17 @@ abstract class ImageProvider<T> {
     // the image we want before getting to this method. We should avoid calling
     // load again, but still update the image cache with LRU information.
     if (stream.completer != null) {
-      final ImageStreamCompleter completer = PaintingBinding.instance.imageCache.putIfAbsent(
+      final ImageStreamCompleter? completer = PaintingBinding.instance!.imageCache!.putIfAbsent(
         key,
-        () => stream.completer,
+        () => stream.completer!,
         onError: handleError,
       );
       assert(identical(completer, stream.completer));
       return;
     }
-    final ImageStreamCompleter completer = PaintingBinding.instance.imageCache.putIfAbsent(
+    final ImageStreamCompleter? completer = PaintingBinding.instance!.imageCache!.putIfAbsent(
       key,
-      () => load(key, PaintingBinding.instance.instantiateImageCodec),
+      () => load(key, PaintingBinding.instance!.instantiateImageCodec),
       onError: handleError,
     );
     if (completer != null) {
@@ -548,10 +549,10 @@ abstract class ImageProvider<T> {
   /// }
   /// ```
   /// {@end-tool}
-  Future<bool> evict({ ImageCache cache, ImageConfiguration configuration = ImageConfiguration.empty }) async {
+  Future<bool> evict({ ImageCache? cache, ImageConfiguration configuration = ImageConfiguration.empty }) async {
     cache ??= imageCache;
     final T key = await obtainKey(configuration);
-    return cache.evict(key);
+    return cache!.evict(key);
   }
 
   /// Converts an ImageProvider's settings plus an ImageConfiguration to a key
@@ -590,9 +591,9 @@ class AssetBundleImageKey {
   ///
   /// The arguments must not be null.
   const AssetBundleImageKey({
-    @required this.bundle,
-    @required this.name,
-    @required this.scale,
+    required this.bundle,
+    required this.name,
+    required this.scale,
   }) : assert(bundle != null),
        assert(name != null),
        assert(scale != null);
@@ -640,7 +641,7 @@ abstract class AssetBundleImageProvider extends ImageProvider<AssetBundleImageKe
   /// image.
   @override
   ImageStreamCompleter load(AssetBundleImageKey key, DecoderCallback decode) {
-    InformationCollector collector;
+    InformationCollector? collector;
     assert(() {
       collector = () sync* {
         yield DiagnosticsProperty<ImageProvider>('Image provider', this);
@@ -662,17 +663,17 @@ abstract class AssetBundleImageProvider extends ImageProvider<AssetBundleImageKe
   /// This function is used by [load].
   @protected
   Future<ui.Codec> _loadAsync(AssetBundleImageKey key, DecoderCallback decode) async {
-    ByteData data;
+    ByteData? data;
     // Hot reload/restart could change whether an asset bundle or key in a
     // bundle are available, or if it is a network backed bundle.
     try {
       data = await key.bundle.load(key.name);
     } on FlutterError {
-      PaintingBinding.instance.imageCache.evict(key);
+      PaintingBinding.instance!.imageCache!.evict(key);
       rethrow;
     }
     if (data == null) {
-      PaintingBinding.instance.imageCache.evict(key);
+      PaintingBinding.instance!.imageCache!.evict(key);
       throw StateError('Unable to read data');
     }
     return await decode(data.buffer.asUint8List());
@@ -685,9 +686,9 @@ class _SizeAwareCacheKey {
 
   final Object providerCacheKey;
 
-  final int width;
+  final int? width;
 
-  final int height;
+  final int? height;
 
   @override
   bool operator ==(Object other) {
@@ -729,10 +730,10 @@ class ResizeImage extends ImageProvider<_SizeAwareCacheKey> {
   final ImageProvider imageProvider;
 
   /// The width the image should decode to and cache.
-  final int width;
+  final int? width;
 
   /// The height the image should decode to and cache.
-  final int height;
+  final int? height;
 
   /// Whether the [width] and [height] parameters should be clamped to the
   /// intrinsic width and height of the image.
@@ -748,7 +749,7 @@ class ResizeImage extends ImageProvider<_SizeAwareCacheKey> {
   ///
   /// When `cacheWidth` and `cacheHeight` are both null, this will return the
   /// `provider` directly.
-  static ImageProvider<dynamic> resizeIfNeeded(int cacheWidth, int cacheHeight, ImageProvider<dynamic> provider) {
+  static ImageProvider<Object> resizeIfNeeded(int? cacheWidth, int? cacheHeight, ImageProvider<Object> provider) {
     if (cacheWidth != null || cacheHeight != null) {
       return ResizeImage(provider, width: cacheWidth, height: cacheHeight);
     }
@@ -757,7 +758,7 @@ class ResizeImage extends ImageProvider<_SizeAwareCacheKey> {
 
   @override
   ImageStreamCompleter load(_SizeAwareCacheKey key, DecoderCallback decode) {
-    final DecoderCallback decodeResize = (Uint8List bytes, {int cacheWidth, int cacheHeight, bool allowUpscaling}) {
+    final DecoderCallback decodeResize = (Uint8List bytes, {int? cacheWidth, int? cacheHeight, bool? allowUpscaling}) {
       assert(
         cacheWidth == null && cacheHeight == null && allowUpscaling == null,
         'ResizeImage cannot be composed with another ImageProvider that applies '
@@ -774,10 +775,10 @@ class ResizeImage extends ImageProvider<_SizeAwareCacheKey> {
 
   @override
   Future<_SizeAwareCacheKey> obtainKey(ImageConfiguration configuration) {
-    Completer<_SizeAwareCacheKey> completer;
+    Completer<_SizeAwareCacheKey>? completer;
     // If the imageProvider.obtainKey future is synchronous, then we will be able to fill in result with
     // a value before completer is initialized below.
-    SynchronousFuture<_SizeAwareCacheKey> result;
+    SynchronousFuture<_SizeAwareCacheKey>? result;
     imageProvider.obtainKey(configuration).then((Object key) {
       if (completer == null) {
         // This future has completed synchronously (completer was never assigned),
@@ -789,7 +790,7 @@ class ResizeImage extends ImageProvider<_SizeAwareCacheKey> {
       }
     });
     if (result != null) {
-      return result;
+      return result!;
     }
     // If the code reaches here, it means the imageProvider.obtainKey was not
     // completed sync, so we initialize the completer for completion later.
@@ -817,7 +818,7 @@ abstract class NetworkImage extends ImageProvider<NetworkImage> {
   /// Creates an object that fetches the image at the given URL.
   ///
   /// The arguments [url] and [scale] must not be null.
-  const factory NetworkImage(String url, { double scale, Map<String, String> headers }) = network_image.NetworkImage;
+  const factory NetworkImage(String url, { double scale, Map<String, String>? headers }) = network_image.NetworkImage;
 
   /// The URL from which the image will be fetched.
   String get url;
@@ -828,7 +829,7 @@ abstract class NetworkImage extends ImageProvider<NetworkImage> {
   /// The HTTP headers that will be used with [HttpClient.get] to fetch image from network.
   ///
   /// When running flutter on the web, headers are not used.
-  Map<String, String> get headers;
+  Map<String, String>? get headers;
 
   @override
   ImageStreamCompleter load(NetworkImage key, DecoderCallback decode);
@@ -870,7 +871,7 @@ class FileImage extends ImageProvider<FileImage> {
       scale: key.scale,
       debugLabel: key.file.path,
       informationCollector: () sync* {
-        yield ErrorDescription('Path: ${file?.path}');
+        yield ErrorDescription('Path: ${file.path}');
       },
     );
   }
@@ -882,7 +883,7 @@ class FileImage extends ImageProvider<FileImage> {
 
     if (bytes.lengthInBytes == 0) {
       // The file may become available later.
-      PaintingBinding.instance.imageCache.evict(key);
+      PaintingBinding.instance!.imageCache!.evict(key);
       throw StateError('$file is empty and cannot be loaded as an image.');
     }
 
@@ -894,15 +895,15 @@ class FileImage extends ImageProvider<FileImage> {
     if (other.runtimeType != runtimeType)
       return false;
     return other is FileImage
-        && other.file?.path == file?.path
+        && other.file.path == file.path
         && other.scale == scale;
   }
 
   @override
-  int get hashCode => hashValues(file?.path, scale);
+  int get hashCode => hashValues(file.path, scale);
 
   @override
-  String toString() => '${objectRuntimeType(this, 'FileImage')}("${file?.path}", scale: $scale)';
+  String toString() => '${objectRuntimeType(this, 'FileImage')}("${file.path}", scale: $scale)';
 }
 
 /// Decodes the given [Uint8List] buffer as an image, associating it with the
@@ -1075,11 +1076,11 @@ class ExactAssetImage extends AssetBundleImageProvider {
   ///
   /// The image is obtained by calling [AssetBundle.load] on the given [bundle]
   /// using the key given by [keyName].
-  final AssetBundle bundle;
+  final AssetBundle? bundle;
 
   /// The name of the package from which the image is included. See the
   /// documentation for the [ExactAssetImage] class itself for details.
-  final String package;
+  final String? package;
 
   @override
   Future<AssetBundleImageKey> obtainKey(ImageConfiguration configuration) {
@@ -1112,10 +1113,10 @@ class _ErrorImageCompleter extends ImageStreamCompleter {
   _ErrorImageCompleter();
 
   void setError({
-    DiagnosticsNode context,
+    DiagnosticsNode? context,
     dynamic exception,
-    StackTrace stack,
-    InformationCollector informationCollector,
+    StackTrace? stack,
+    InformationCollector? informationCollector,
     bool silent = false,
   }) {
     reportError(
@@ -1132,7 +1133,7 @@ class _ErrorImageCompleter extends ImageStreamCompleter {
 class NetworkImageLoadException implements Exception {
   /// Creates a [NetworkImageLoadException] with the specified http [statusCode]
   /// and [uri].
-  NetworkImageLoadException({@required this.statusCode, @required this.uri})
+  NetworkImageLoadException({required this.statusCode, required this.uri})
       : assert(uri != null),
         assert(statusCode != null),
         _message = 'HTTP request failed, statusCode: $statusCode, $uri';