fix nullability of parameters with redirecting factory constructors (#71547)

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

@@ -176,31 +176,31 @@ class FlatButton extends MaterialButton {
   ///
   /// The [icon], [label], and [clipBehavior] arguments must not be null.
   factory FlatButton.icon({
-    Key key,
-    required VoidCallback onPressed,
-    VoidCallback onLongPress,
-    ValueChanged<bool> onHighlightChanged,
-    MouseCursor mouseCursor,
-    ButtonTextTheme textTheme,
-    Color textColor,
-    Color disabledTextColor,
-    Color color,
-    Color disabledColor,
-    Color focusColor,
-    Color hoverColor,
-    Color highlightColor,
-    Color splashColor,
-    Brightness colorBrightness,
-    EdgeInsetsGeometry padding,
-    ShapeBorder shape,
+    Key? key,
+    required VoidCallback? onPressed,
+    VoidCallback? onLongPress,
+    ValueChanged<bool>? onHighlightChanged,
+    MouseCursor? mouseCursor,
+    ButtonTextTheme? textTheme,
+    Color? textColor,
+    Color? disabledTextColor,
+    Color? color,
+    Color? disabledColor,
+    Color? focusColor,
+    Color? hoverColor,
+    Color? highlightColor,
+    Color? splashColor,
+    Brightness? colorBrightness,
+    EdgeInsetsGeometry? padding,
+    ShapeBorder? shape,
     Clip clipBehavior,
-    FocusNode focusNode,
+    FocusNode? focusNode,
     bool autofocus,
-    MaterialTapTargetSize materialTapTargetSize,
+    MaterialTapTargetSize? materialTapTargetSize,
     required Widget icon,
     required Widget label,
-    double minWidth,
-    double height,
+    double? minWidth,
+    double? height,
   }) = _FlatButtonWithIcon;
 
   @override

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

@@ -196,31 +196,31 @@ class RaisedButton extends MaterialButton {
   /// The [elevation], [highlightElevation], [disabledElevation], [icon],
   /// [label], and [clipBehavior] arguments must not be null.
   factory RaisedButton.icon({
-    Key key,
-    required VoidCallback onPressed,
-    VoidCallback onLongPress,
-    ValueChanged<bool> onHighlightChanged,
-    MouseCursor mouseCursor,
-    ButtonTextTheme textTheme,
-    Color textColor,
-    Color disabledTextColor,
-    Color color,
-    Color disabledColor,
-    Color focusColor,
-    Color hoverColor,
-    Color highlightColor,
-    Color splashColor,
-    Brightness colorBrightness,
-    double elevation,
-    double highlightElevation,
-    double disabledElevation,
-    ShapeBorder shape,
+    Key? key,
+    required VoidCallback? onPressed,
+    VoidCallback? onLongPress,
+    ValueChanged<bool>? onHighlightChanged,
+    MouseCursor? mouseCursor,
+    ButtonTextTheme? textTheme,
+    Color? textColor,
+    Color? disabledTextColor,
+    Color? color,
+    Color? disabledColor,
+    Color? focusColor,
+    Color? hoverColor,
+    Color? highlightColor,
+    Color? splashColor,
+    Brightness? colorBrightness,
+    double? elevation,
+    double? highlightElevation,
+    double? disabledElevation,
+    ShapeBorder? shape,
     Clip clipBehavior,
-    FocusNode focusNode,
+    FocusNode? focusNode,
     bool autofocus,
-    EdgeInsetsGeometry padding,
-    MaterialTapTargetSize materialTapTargetSize,
-    Duration animationDuration,
+    EdgeInsetsGeometry? padding,
+    MaterialTapTargetSize? materialTapTargetSize,
+    Duration? animationDuration,
     required Widget icon,
     required Widget label,
   }) = _RaisedButtonWithIcon;
@@ -276,7 +276,7 @@ class RaisedButton extends MaterialButton {
 class _RaisedButtonWithIcon extends RaisedButton with MaterialButtonWithIconMixin {
   _RaisedButtonWithIcon({
     Key? key,
-    required VoidCallback onPressed,
+    required VoidCallback? onPressed,
     VoidCallback? onLongPress,
     ValueChanged<bool>? onHighlightChanged,
     MouseCursor? mouseCursor,

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

@@ -96,12 +96,12 @@ class Typography with Diagnosticable {
     'This feature was deprecated after v1.13.8.'
   )
   factory Typography({
-    TargetPlatform platform,
-    TextTheme black,
-    TextTheme white,
-    TextTheme englishLike,
-    TextTheme dense,
-    TextTheme tall,
+    TargetPlatform? platform,
+    TextTheme? black,
+    TextTheme? white,
+    TextTheme? englishLike,
+    TextTheme? dense,
+    TextTheme? tall,
   }) = Typography.material2014;
 
   /// Creates a typography instance using material design's 2014 defaults.