Form sample crashes with "No Material widget found"

[nbros]

I tried the sample from:
https://api.flutter.dev/flutter/widgets/Form-class.html

The TextFormField in this sample triggers an error in the Flutter framework:

flutter/packages/flutter/lib/src/widgets/form.dart

Line 33 in ce6dedf

/// TextFormField(

I/flutter (15706): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter (15706): The following assertion was thrown building TextField(controller:
I/flutter (15706): TextEditingController#7d7e5(TextEditingValue(text: ┤├, selection: TextSelection(baseOffset: -1,
I/flutter (15706): extentOffset: -1, affinity: TextAffinity.downstream, isDirectional: false), composing:
I/flutter (15706): TextRange(start: -1, end: -1))), enabled: true, decoration: InputDecoration(alignLabelWithHint:
I/flutter (15706): false), dirty, state: _TextFieldState#02305):
I/flutter (15706): No Material widget found.
I/flutter (15706): TextField widgets require a Material widget ancestor.
I/flutter (15706): In material design, most widgets are conceptually "printed" on a sheet of material. In Flutter's
I/flutter (15706): material library, that material is represented by the Material widget. It is the Material widget
I/flutter (15706): that renders ink splashes, for instance. Because of this, many material library widgets require that
I/flutter (15706): there be a Material widget in the tree above them.
I/flutter (15706): To introduce a Material widget, you can either directly include one, or use a widget that contains
I/flutter (15706): Material itself, such as a Card, Dialog, Drawer, or Scaffold.
I/flutter (15706): The specific widget that could not find a Material ancestor was:
I/flutter (15706):   TextField(controller: TextEditingController#7d7e5(TextEditingValue(text: ┤├, selection:
I/flutter (15706): TextSelection(baseOffset: -1, extentOffset: -1, affinity: TextAffinity.downstream, isDirectional:
I/flutter (15706): false), composing: TextRange(start: -1, end: -1))), enabled: true, decoration:
I/flutter (15706): InputDecoration(alignLabelWithHint: false))
I/flutter (15706): The ancestors of this widget were:
I/flutter (15706):   TextFormField
I/flutter (15706):   Column(direction: vertical, mainAxisAlignment: start, crossAxisAlignment: start)
I/flutter (15706):   _FormScope
I/flutter (15706):   WillPopScope
I/flutter (15706):   Form-[LabeledGlobalKey<FormState>#55011]
I/flutter (15706):   MyStatefulWidget
I/flutter (15706):   Semantics(container: false, properties: SemanticsProperties, label: null, value: null, hint: null,
I/flutter (15706): hintOverrides: null)
I/flutter (15706):   Builder
I/flutter (15706):   RepaintBoundary-[GlobalKey#c3349]
I/flutter (15706):   IgnorePointer(ignoring: false)
I/flutter (15706):   FadeTransition(opacity: AnimationController#33a1f(⏭ 1.000; paused; for
I/flutter (15706): MaterialPageRoute<dynamic>(/))➩ProxyAnimation➩CurveTween(curve: Cubic(0.42, 0.00, 1.00, 1.00))➩1.0)
I/flutter (15706):   FractionalTranslation
I/flutter (15706):   SlideTransition(animation: AnimationController#33a1f(⏭ 1.000; paused; for
I/flutter (15706): MaterialPageRoute<dynamic>(/))➩ProxyAnimation➩CurveTween(curve: Cubic(0.40, 0.00, 0.20,
I/flutter (15706): 1.00))➩Tween<Offset>(Offset(0.0, 0.3) → Offset(0.0, 0.0))➩Offset(0.0, 0.0))
I/flutter (15706):   _FadeUpwardsPageTransition
I/flutter (15706):   AnimatedBuilder(animation: Listenable.merge([AnimationController#33a1f(⏭ 1.000; paused; for
I/flutter (15706): MaterialPageRoute<dynamic>(/))➩ProxyAnimation,
I/flutter (15706): kAlwaysDismissedAnimation➩ProxyAnimation➩ProxyAnimation]))
I/flutter (15706):   RepaintBoundary
I/flutter (15706):   _FocusMarker
I/flutter (15706):   Semantics(container: false, properties: SemanticsProperties, label: null, value: null, hint: null,
I/flutter (15706): hintOverrides: null)
I/flutter (15706):   FocusScope(node: FocusScopeNode#0bc35)
I/flutter (15706):   PageStorage
I/flutter (15706):   Offstage(offstage: false)
I/flutter (15706):   _ModalScopeStatus(active)
I/flutter (15706):   _ModalScope<dynamic>-[LabeledGlobalKey<_ModalScopeState<dynamic>>#94d9f]
I/flutter (15706):   _OverlayEntry-[LabeledGlobalKey<_OverlayEntryState>#40f24]
I/flutter (15706):   Stack(alignment: AlignmentDirectional.topStart, fit: expand, overflow: clip)
I/flutter (15706):   _Theatre
I/flutter (15706):   Overlay-[LabeledGlobalKey<OverlayState>#adc1c]
I/flutter (15706):   _FocusMarker
I/flutter (15706):   Semantics(container: false, properties: SemanticsProperties, label: null, value: null, hint: null,
I/flutter (15706): hintOverrides: null)
I/flutter (15706):   FocusScope(AUTOFOCUS, node: FocusScopeNode#903ba)
I/flutter (15706):   AbsorbPointer(absorbing: false)
I/flutter (15706):   Listener(listeners: [down, up, cancel], behavior: deferToChild)
I/flutter (15706):   Navigator-[GlobalObjectKey<NavigatorState> _WidgetsAppState#89300]
I/flutter (15706):   IconTheme(IconThemeData#2abdc(color: Color(0xdd000000)))
I/flutter (15706):   IconTheme(IconThemeData#6140b(color: MaterialColor(primary value: Color(0xff2196f3))))
I/flutter (15706):   _InheritedCupertinoTheme
I/flutter (15706):   CupertinoTheme
I/flutter (15706):   _InheritedTheme
I/flutter (15706):   Theme(ThemeData#8a43c(buttonTheme: ButtonThemeData#7ffbc(buttonColor: Color(0xffe0e0e0),
I/flutter (15706): focusColor: Color(0x1f000000), hoverColor: Color(0x0a000000), colorScheme:
I/flutter (15706): ColorScheme#23964(primary: MaterialColor(primary value: Color(0xff2196f3)), primaryVariant:
I/flutter (15706): Color(0xff1976d2), secondary: Color(0xff2196f3), secondaryVariant: Color(0xff1976d2), background:
I/flutter (15706): Color(0xff90caf9), error: Color(0xffd32f2f), onSecondary: Color(0xffffffff), onBackground:
I/flutter (15706): Color(0xffffffff)), materialTapTargetSize: MaterialTapTargetSize.padded), textTheme:
I/flutter (15706): TextTheme#0bd0d, primaryTextTheme: TextTheme#b9877(display4: TextStyle(debugLabel: whiteMountainView
I/flutter (15706): display4, inherit: true, color: Color(0xb3ffffff), family: Roboto, decoration: TextDecoration.none),
I/flutter (15706): display3: TextStyle(debugLabel: whiteMountainView display3, inherit: true, color: Color(0xb3ffffff),
I/flutter (15706): family: Roboto, decoration: TextDecoration.none), display2: TextStyle(debugLabel: whiteMountainView
I/flutter (15706): display2, inherit: true, color: Color(0xb3ffffff), family: Roboto, decoration: TextDecoration.none),
I/flutter (15706): display1: TextStyle(debugLabel: whiteMountainView display1, inherit: true, color: Color(0xb3ffffff),
I/flutter (15706): family: Roboto, decoration: TextDecoration.none), headline: TextStyle(debugLabel: whiteMountainView
I/flutter (15706): headline, inherit: true, color: Color(0xffffffff), family: Roboto, decoration: TextDecoration.none),
I/flutter (15706): title: TextStyle(debugLabel: whiteMountainView title, inherit: true, color: Color(0xffffffff),
I/flutter (15706): family: Roboto, decoration: TextDecoration.none), subhead: TextStyle(debugLabel: whiteMountainView
I/flutter (15706): subhead, inherit: true, color: Color(0xffffffff), family: Roboto, decoration: TextDecoration.none),
I/flutter (15706): body2: TextStyle(debugLabel: whiteMountainView body2, inherit: true, color: Color(0xffffffff),
I/flutter (15706): family: Roboto, decoration: TextDecoration.none), body1: TextStyle(debugLabel: whiteMountainView
I/flutter (15706): body1, inherit: true, color: Color(0xffffffff), family: Roboto, decoration: TextDecoration.none),
I/flutter (15706): caption: TextStyle(debugLabel: whiteMountainView caption, inherit: true, color: Color(0xb3ffffff),
I/flutter (15706): family: Roboto, decoration: TextDecoration.none), button: TextStyle(debugLabel: whiteMountainView
I/flutter (15706): button, inherit: true, color: Color(0xffffffff), family: Roboto, decoration: TextDecoration.none),
I/flutter (15706): subtitle): TextStyle(debugLabel: whiteMountainView subtitle, inherit: true, color:
I/flutter (15706): Color(0xffffffff), family: Roboto, decoration: TextDecoration.none), overline: TextStyle(debugLabel:
I/flutter (15706): whiteMountainView overline, inherit: true, color: Color(0xffffffff), family: Roboto, decoration:
I/flutter (15706): TextDecoration.none)), accentTextTheme: TextTheme#b9877(display4: TextStyle(debugLabel:
I/flutter (15706): whiteMountainView display4, inherit: true, color: Color(0xb3ffffff), family: Roboto, decoration:
I/flutter (15706): TextDecoration.none), display3: TextStyle(debugLabel: whiteMountainView display3, inherit: true,
I/flutter (15706): color: Color(0xb3ffffff), family: Roboto, decoration: TextDecoration.none), display2:
I/flutter (15706): TextStyle(debugLabel: whiteMountainView display2, inherit: true, color: Color(0xb3ffffff), family:
I/flutter (15706): Roboto, decoration: TextDecoration.none), display1: TextStyle(debugLabel: whiteMountainView
I/flutter (15706): display1, inherit: true, color: Color(0xb3ffffff), family: Roboto, decoration: TextDecoration.none),
I/flutter (15706): headline: TextStyle(debugLabel: whiteMountainView headline, inherit: true, color: Color(0xffffffff),
I/flutter (15706): family: Roboto, decoration: TextDecoration.none), title: TextStyle(debugLabel: whiteMountainView
I/flutter (15706): title, inherit: true, color: Color(0xffffffff), family: Roboto, decoration: TextDecoration.none),
I/flutter (15706): subhead: TextStyle(debugLabel: whiteMountainView subhead, inherit: true, color: Color(0xffffffff),
I/flutter (15706): family: Roboto, decoration: TextDecoration.none), body2: TextStyle(debugLabel: whiteMountainView
I/flutter (15706): body2, inherit: true, color: Color(0xffffffff), family: Roboto, decoration: TextDecoration.none),
I/flutter (15706): body1: TextStyle(debugLabel: whiteMountainView body1, inherit: true, color: Color(0xffffffff),
I/flutter (15706): family: Roboto, decoration: TextDecoration.none), caption: TextStyle(debugLabel: whiteMountainView
I/flutter (15706): caption, inherit: true, color: Color(0xb3ffffff), family: Roboto, decoration: TextDecoration.none),
I/flutter (15706): button: TextStyle(debugLabel: whiteMountainView button, inherit: true, color: Color(0xffffffff),
I/flutter (15706): family: Roboto, decoration: TextDecoration.none), subtitle): TextStyle(debugLabel: whiteMountainView
I/flutter (15706): subtitle, inherit: true, color: Color(0xffffffff), family: Roboto, decoration: TextDecoration.none),
I/flutter (15706): overline: TextStyle(debugLabel: whiteMountainView overline, inherit: true, color: Color(0xffffffff),
I/flutter (15706): family: Roboto, decoration: TextDecoration.none)), inputDecorationTheme: InputDecorationTheme#21974,
I/flutter (15706): iconTheme: IconThemeData#2abdc(color: Color(0xdd000000)), primaryIconTheme:
I/flutter (15706): IconThemeData#15fa8(color: Color(0xffffffff)), accentIconTheme: IconThemeData#15fa8(color:
I/flutter (15706): Color(0xffffffff)), sliderTheme: SliderThemeData#1ddfc, tabBarTheme: TabBarTheme#50f35, cardTheme:
I/flutter (15706): CardTheme#b4e63, chipTheme: ChipThemeData#1f810, materialTapTargetSize:
I/flutter (15706): MaterialTapTargetSize.padded, pageTransitionsTheme: PageTransitionsTheme#aba6e))
I/flutter (15706):   AnimatedTheme(duration: 200ms)
I/flutter (15706):   Builder
I/flutter (15706):   DefaultTextStyle(debugLabel: fallback style; consider putting your text in a Material, inherit:
I/flutter (15706): true, color: Color(0xd0ff0000), family: monospace, size: 48.0, weight: 900, decoration: double
I/flutter (15706): Color(0xffffff00) TextDecoration.underline, softWrap: wrapping at box width, overflow: clip)
I/flutter (15706):   CustomPaint
I/flutter (15706):   Banner("DEBUG", textDirection: ltr, location: topEnd, Color(0xa0b71c1c), text inherit: true, text
I/flutter (15706): color: Color(0xffffffff), text size: 10.2, text weight: 900, text height: 1.0x)
I/flutter (15706):   CheckedModeBanner("DEBUG")
I/flutter (15706):   Title(title: "Flutter Code Sample", color: MaterialColor(primary value: Color(0xff2196f3)))
I/flutter (15706):   Directionality(textDirection: ltr)
I/flutter (15706):   _LocalizationsScope-[GlobalKey#f71b8]
I/flutter (15706):   Semantics(container: false, properties: SemanticsProperties, label: null, value: null, hint: null,
I/flutter (15706): textDirection: ltr, hintOverrides: null)
I/flutter (15706):   Localizations(locale: en_US, delegates: [DefaultMaterialLocalizations.delegate(en_US),
I/flutter (15706): DefaultCupertinoLocalizations.delegate(en_US), DefaultWidgetsLocalizations.delegate(en_US)])
I/flutter (15706):   MediaQuery(MediaQueryData(size: Size(411.4, 683.4), devicePixelRatio: 2.6, textScaleFactor: 1.0,
I/flutter (15706): platformBrightness: Brightness.light, padding: EdgeInsets(0.0, 24.0, 0.0, 0.0), viewPadding:
I/flutter (15706): EdgeInsets(0.0, 24.0, 0.0, 0.0), viewInsets: EdgeInsets.zero, alwaysUse24HourFormat: false,
I/flutter (15706): accessibleNavigation: false, disableAnimations: false, invertColors: false, boldText: false))
I/flutter (15706):   DefaultFocusTraversal
I/flutter (15706):   WidgetsApp-[GlobalObjectKey _MaterialAppState#ccbfb]
I/flutter (15706):   ScrollConfiguration(behavior: _MaterialScrollBehavior)
I/flutter (15706):   MaterialApp
I/flutter (15706):   MyApp
I/flutter (15706):   [root]
I/flutter (15706):
I/flutter (15706): When the exception was thrown, this was the stack:
�[38;5;244mI/flutter (15706): #0      debugCheckHasMaterial.<anonymous closure>�[39;49m
�[38;5;244mI/flutter (15706): #1      debugCheckHasMaterial�[39;49m
�[38;5;244mI/flutter (15706): #2      _TextFieldState.build�[39;49m
�[38;5;244mI/flutter (15706): #3      StatefulElement.build�[39;49m
�[38;5;244mI/flutter (15706): #4      ComponentElement.performRebuild�[39;49m
�[38;5;244mI/flutter (15706): #5      Element.rebuild�[39;49m
�[38;5;244mI/flutter (15706): #6      StatefulElement.update�[39;49m
�[38;5;244mI/flutter (15706): #7      Element.updateChild�[39;49m
�[38;5;244mI/flutter (15706): #8      ComponentElement.performRebuild�[39;49m
�[38;5;244mI/flutter (15706): #9      Element.rebuild�[39;49m
�[38;5;244mI/flutter (15706): #10     StatefulElement.update�[39;49m
�[38;5;244mI/flutter (15706): #11     Element.updateChild�[39;49m
�[38;5;244mI/flutter (15706): #12     RenderObjectElement.updateChildren�[39;49m
�[38;5;244mI/flutter (15706): #13     MultiChildRenderObjectElement.update�[39;49m
�[38;5;244mI/flutter (15706): #14     Element.updateChild�[39;49m
�[38;5;244mI/flutter (15706): #15     ComponentElement.performRebuild�[39;49m
�[38;5;244mI/flutter (15706): #16     Element.rebuild�[39;49m
�[38;5;244mI/flutter (15706): #17     ProxyElement.update�[39;49m
�[38;5;244mI/flutter (15706): #18     Element.updateChild�[39;49m
�[38;5;244mI/flutter (15706): #19     ComponentElement.performRebuild�[39;49m
�[38;5;244mI/flutter (15706): #20     Element.rebuild�[39;49m
�[38;5;244mI/flutter (15706): #21     StatefulElement.update�[39;49m
�[38;5;244mI/flutter (15706): #22     Element.updateChild�[39;49m
�[38;5;244mI/flutter (15706): #23     ComponentElement.performRebuild�[39;49m
�[38;5;244mI/flutter (15706): #24     Element.rebuild�[39;49m
�[38;5;244mI/flutter (15706): #25     StatefulElement.update�[39;49m
�[38;5;244mI/flutter (15706): #26     Element.updateChild�[39;49m
Reloaded 0 of 455 libraries in 277ms.
�[38;5;244mI/flutter (15706): #27     ComponentElement.performRebuild�[39;49m
�[38;5;244mI/flutter (15706): #28     Element.rebuild�[39;49m
�[38;5;244mI/flutter (15706): #29     StatefulElement.update�[39;49m
�[38;5;244mI/flutter (15706): #30     Element.updateChild�[39;49m
�[38;5;244mI/flutter (15706): #31     SingleChildRenderObjectElement.update�[39;49m
�[38;5;244mI/flutter (15706): #32     Element.updateChild�[39;49m
�[38;5;244mI/flutter (15706): #33     ComponentElement.performRebuild�[39;49m
�[38;5;244mI/flutter (15706): #34     Element.rebuild�[39;49m
�[38;5;244mI/flutter (15706): #35     StatelessElement.update�[39;49m
�[38;5;244mI/flutter (15706): #36     Element.updateChild�[39;49m
�[38;5;244mI/flutter (15706): #37     SingleChildRenderObjectElement.update�[39;49m
�[38;5;244mI/flutter (15706): #38     Element.updateChild�[39;49m
�[38;5;244mI/flutter (15706): #39     SingleChildRenderObjectElement.update�[39;49m
�[38;5;244mI/flutter (15706): #40     Element.updateChild�[39;49m
�[38;5;244mI/flutter (15706): #41     SingleChildRenderObjectElement.update�[39;49m
�[38;5;244mI/flutter (15706): #42     Element.updateChild�[39;49m
�[38;5;244mI/flutter (15706): #43     SingleChildRenderObjectElement.update�[39;49m
�[38;5;244mI/flutter (15706): #44     Element.updateChild�[39;49m
�[38;5;244mI/flutter (15706): #45     ComponentElement.performRebuild�[39;49m
�[38;5;244mI/flutter (15706): #46     Element.rebuild�[39;49m
�[38;5;244mI/flutter (15706): #47     StatefulElement.update�[39;49m
�[38;5;244mI/flutter (15706): #48     Element.updateChild�[39;49m
�[38;5;244mI/flutter (15706): #49     ComponentElement.performRebuild�[39;49m
�[38;5;244mI/flutter (15706): #50     Element.rebuild�[39;49m
�[38;5;244mI/flutter (15706): #51     StatelessElement.update�[39;49m
�[38;5;244mI/flutter (15706): #52     Element.updateChild�[39;49m
�[38;5;244mI/flutter (15706): #53     ComponentElement.performRebuild�[39;49m
�[38;5;244mI/flutter (15706): #54     Element.rebuild�[39;49m
�[38;5;244mI/flutter (15706): #55     StatefulElement.update�[39;49m
�[38;5;244mI/flutter (15706): #56     Element.updateChild�[39;49m
�[38;5;244mI/flutter (15706): #57     SingleChildRenderObjectElement.update�[39;49m
�[38;5;244mI/flutter (15706): #58     Element.updateChild�[39;49m
�[38;5;244mI/flutter (15706): #59     ComponentElement.performRebuild�[39;49m
�[38;5;244mI/flutter (15706): #60     Element.rebuild�[39;49m
�[38;5;244mI/flutter (15706): #61     ProxyElement.update�[39;49m
�[38;5;244mI/flutter (15706): #62     _InheritedNotifierElement.update�[39;49m
�[38;5;244mI/flutter (15706): #63     Element.updateChild�[39;49m
�[38;5;244mI/flutter (15706): #64     SingleChildRenderObjectElement.update�[39;49m
�[38;5;244mI/flutter (15706): #65     Element.updateChild�[39;49m
�[38;5;244mI/flutter (15706): #66     ComponentElement.performRebuild�[39;49m
�[38;5;244mI/flutter (15706): #67     Element.rebuild�[39;49m
�[38;5;244mI/flutter (15706): #68     StatefulElement.update�[39;49m
�[38;5;244mI/flutter (15706): #69     Element.updateChild�[39;49m
�[38;5;244mI/flutter (15706): #70     ComponentElement.performRebuild�[39;49m
�[38;5;244mI/flutter (15706): #71     Element.rebuild�[39;49m
�[38;5;244mI/flutter (15706): #72     StatelessElement.update�[39;49m
�[38;5;244mI/flutter (15706): #73     Element.updateChild�[39;49m
�[38;5;244mI/flutter (15706): #74     SingleChildRenderObjectElement.update�[39;49m
�[38;5;244mI/flutter (15706): #75     Element.updateChild�[39;49m
�[38;5;244mI/flutter (15706): #76     ComponentElement.performRebuild�[39;49m
�[38;5;244mI/flutter (15706): #77     Element.rebuild�[39;49m
�[38;5;244mI/flutter (15706): #78     ProxyElement.update�[39;49m
�[38;5;244mI/flutter (15706): #79     Element.updateChild�[39;49m
�[38;5;244mI/flutter (15706): #80     ComponentElement.performRebuild�[39;49m
�[38;5;244mI/flutter (15706): #81     Element.rebuild�[39;49m
�[38;5;244mI/flutter (15706): #82     BuildOwner.buildScope�[39;49m
�[38;5;244mI/flutter (15706): #83     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding&WidgetsBinding.drawFrame�[39;49m
�[38;5;244mI/flutter (15706): #84     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding._handlePersistentFrameCallback�[39;49m
�[38;5;244mI/flutter (15706): #85     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback�[39;49m
�[38;5;244mI/flutter (15706): #86     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame�[39;49m
�[38;5;244mI/flutter (15706): #87     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.scheduleWarmUpFrame.<anonymous closure>�[39;49m
�[38;5;244mI/flutter (15706): #89     _Timer._runTimers  (dart:isolate-patch/timer_impl.dart:382:19)�[39;49m
�[38;5;244mI/flutter (15706): #90     _Timer._handleMessage  (dart:isolate-patch/timer_impl.dart:416:5)�[39;49m
�[38;5;244mI/flutter (15706): #91     _RawReceivePortImpl._handleMessage  (dart:isolate-patch/isolate_patch.dart:172:12)�[39;49m
I/flutter (15706): (elided one frame from package dart:async-patch)
I/flutter (15706): ════════════════════════════════════════════════════════════════════════════════════════════════════
I/flutter (15706): Another exception was thrown: A RenderFlex overflowed by 99397 pixels on the bottom.

[nbros]

To import the code I used Visual Studio Code :

[nbros]

The sample works if I add a Scaffold around MyStatefulWidget, so maybe the sample code should include a Scaffold?

[melwinlobo18]

The error description clearly says that:

No Material widget found.

TextField widgets require a Material widget ancestor.

In material design, most widgets are conceptually "printed" on a sheet of material. 
In Flutter's material library, that material is represented by the Material widget.
It is the Material widget that renders ink splashes, for instance. Because of this, 
many material library widgets require that there be a Material widget in the tree 
above them.

To introduce a Material widget, you can either directly include one, or use a widget
that contains the material itself, such as a Card, Dialog, Drawer, or Scaffold.

[nbros]

Yes exactly, the sample code should be fixed by adding a material widget ancestor so that it works out of the box.

[shihaohong]

It seems that this has already been fixed but has not made it into master yet. See https://master-api.flutter.dev/flutter/widgets/Form-class.html for the fixed doc, and see #35892 for the fix.

[github-actions]

This thread has been automatically locked since there has not been any recent activity after it was closed. If you are still experiencing a similar issue, please open a new bug, including the output of flutter doctor -v and a minimal reproduction of the issue.