<h2 dir="auto">Steps to Reproduce</h2>
<p dir="auto">Here's a sample app which demonstrates the problem, you can trigger the error by switching between the tabs. For example selecting the 3rd tab and then the 1st tab.</p>
<div class="highlight highlight-source-dart notranslate position-relative overflow-auto" dir="auto" data-snippet-clipboard-copy-content="import 'package:flutter/material.dart';

void main() =&gt; runApp(new MyApp());

class MyApp extends StatefulWidget {

  @override
  _MyAppState createState() =&gt; new _MyAppState();
}

class _MyAppState extends State&lt;MyApp&gt; with SingleTickerProviderStateMixin {

  TabController _controller;

  @override
  void initState() {
    super.initState();
    _controller = new TabController(vsync: this, length:3);
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      home: new Scaffold(
        appBar: new AppBar(
          title: new Text('Sample App'),
          bottom: TabBar(
            controller: _controller,
            isScrollable: true,
            tabs: [
              Tab(
                text: 'Page 1',
              ),
              Tab(
                text: 'Page 2',
              ),
              Tab(
                text: 'Page 3',
              ),
            ],
          ),
        ),
        body: TabBarView(
          controller: _controller,
          children: &lt;Widget&gt;[
            Page1(),
            Page2(),
            Page3(),
          ],
        ),
      ),
    );
  }
}

class Page1 extends StatefulWidget {

  static final GlobalKey&lt;FormFieldState&lt;String&gt;&gt; value1Key = GlobalKey&lt;FormFieldState&lt;String&gt;&gt;();

  @override
  _Page1State createState() =&gt; new _Page1State();
}

class _Page1State extends State&lt;Page1&gt; with AutomaticKeepAliveClientMixin {
  @override
  bool get wantKeepAlive =&gt; true;

  @override
  Widget build(BuildContext context) {
    return TextFormField(
      key: Page1.value1Key,
    );
  }
}

class Page2 extends StatefulWidget {

  static final GlobalKey&lt;FormFieldState&lt;String&gt;&gt; value2Key = GlobalKey&lt;FormFieldState&lt;String&gt;&gt;();

  @override
  _Page2State createState() =&gt; new _Page2State();
}

class _Page2State extends State&lt;Page2&gt; with AutomaticKeepAliveClientMixin {
  @override
  bool get wantKeepAlive =&gt; true;

  @override
  Widget build(BuildContext context) {
    return TextFormField(
      key: Page2.value2Key,
    );
  }
}

class Page3 extends StatefulWidget {

  static final GlobalKey&lt;FormFieldState&lt;String&gt;&gt; value3Key = GlobalKey&lt;FormFieldState&lt;String&gt;&gt;();

  @override
  _Page3State createState() =&gt; new _Page3State();
}

class _Page3State extends State&lt;Page3&gt; with AutomaticKeepAliveClientMixin {
  @override
  bool get wantKeepAlive =&gt; true;

  @override
  Widget build(BuildContext context) {
    return TextFormField(
      key: Page3.value3Key,
    );
  }
}"><pre class="notranslate"><span class="pl-k">import</span> <span class="pl-s">'package:flutter/material.dart'</span>;

<span class="pl-k">void</span> <span class="pl-en">main</span>() <span class="pl-k">=&gt;</span> <span class="pl-en">runApp</span>(<span class="pl-k">new</span> <span class="pl-c1">MyApp</span>());

<span class="pl-k">class</span> <span class="pl-c1">MyApp</span> <span class="pl-k">extends</span> <span class="pl-c1">StatefulWidget</span> {

  <span class="pl-k">@override</span>
  <span class="pl-c1">_MyAppState</span> <span class="pl-en">createState</span>() <span class="pl-k">=&gt;</span> <span class="pl-k">new</span> <span class="pl-c1">_MyAppState</span>();
}

<span class="pl-k">class</span> <span class="pl-c1">_MyAppState</span> <span class="pl-k">extends</span> <span class="pl-c1">State</span>&lt;<span class="pl-c1">MyApp</span>&gt; <span class="pl-k">with</span> <span class="pl-c1">SingleTickerProviderStateMixin</span> {

  <span class="pl-c1">TabController</span> _controller;

  <span class="pl-k">@override</span>
  <span class="pl-k">void</span> <span class="pl-en">initState</span>() {
    <span class="pl-c1">super</span>.<span class="pl-en">initState</span>();
    _controller <span class="pl-k">=</span> <span class="pl-k">new</span> <span class="pl-c1">TabController</span>(vsync<span class="pl-k">:</span> <span class="pl-c1">this</span>, length<span class="pl-k">:</span><span class="pl-c1">3</span>);
  }

  <span class="pl-k">@override</span>
  <span class="pl-k">void</span> <span class="pl-en">dispose</span>() {
    _controller.<span class="pl-en">dispose</span>();
    <span class="pl-c1">super</span>.<span class="pl-en">dispose</span>();
  }

  <span class="pl-k">@override</span>
  <span class="pl-c1">Widget</span> <span class="pl-en">build</span>(<span class="pl-c1">BuildContext</span> context) {
    <span class="pl-k">return</span> <span class="pl-k">new</span> <span class="pl-c1">MaterialApp</span>(
      home<span class="pl-k">:</span> <span class="pl-k">new</span> <span class="pl-c1">Scaffold</span>(
        appBar<span class="pl-k">:</span> <span class="pl-k">new</span> <span class="pl-c1">AppBar</span>(
          title<span class="pl-k">:</span> <span class="pl-k">new</span> <span class="pl-c1">Text</span>(<span class="pl-s">'Sample App'</span>),
          bottom<span class="pl-k">:</span> <span class="pl-c1">TabBar</span>(
            controller<span class="pl-k">:</span> _controller,
            isScrollable<span class="pl-k">:</span> <span class="pl-c1">true</span>,
            tabs<span class="pl-k">:</span> [
              <span class="pl-c1">Tab</span>(
                text<span class="pl-k">:</span> <span class="pl-s">'Page 1'</span>,
              ),
              <span class="pl-c1">Tab</span>(
                text<span class="pl-k">:</span> <span class="pl-s">'Page 2'</span>,
              ),
              <span class="pl-c1">Tab</span>(
                text<span class="pl-k">:</span> <span class="pl-s">'Page 3'</span>,
              ),
            ],
          ),
        ),
        body<span class="pl-k">:</span> <span class="pl-c1">TabBarView</span>(
          controller<span class="pl-k">:</span> _controller,
          children<span class="pl-k">:</span> <span class="pl-k">&lt;</span><span class="pl-c1">Widget</span><span class="pl-k">&gt;</span>[
            <span class="pl-c1">Page1</span>(),
            <span class="pl-c1">Page2</span>(),
            <span class="pl-c1">Page3</span>(),
          ],
        ),
      ),
    );
  }
}

<span class="pl-k">class</span> <span class="pl-c1">Page1</span> <span class="pl-k">extends</span> <span class="pl-c1">StatefulWidget</span> {

  <span class="pl-k">static</span> <span class="pl-k">final</span> <span class="pl-c1">GlobalKey</span>&lt;<span class="pl-c1">FormFieldState</span>&lt;<span class="pl-c1">String</span>&gt;&gt; value1Key <span class="pl-k">=</span> <span class="pl-c1">GlobalKey</span>&lt;<span class="pl-c1">FormFieldState</span>&lt;<span class="pl-c1">String</span>&gt;&gt;();

  <span class="pl-k">@override</span>
  <span class="pl-c1">_Page1State</span> <span class="pl-en">createState</span>() <span class="pl-k">=&gt;</span> <span class="pl-k">new</span> <span class="pl-c1">_Page1State</span>();
}

<span class="pl-k">class</span> <span class="pl-c1">_Page1State</span> <span class="pl-k">extends</span> <span class="pl-c1">State</span>&lt;<span class="pl-c1">Page1</span>&gt; <span class="pl-k">with</span> <span class="pl-c1">AutomaticKeepAliveClientMixin</span> {
  <span class="pl-k">@override</span>
  <span class="pl-c1">bool</span> <span class="pl-k">get</span> wantKeepAlive <span class="pl-k">=&gt;</span> <span class="pl-c1">true</span>;

  <span class="pl-k">@override</span>
  <span class="pl-c1">Widget</span> <span class="pl-en">build</span>(<span class="pl-c1">BuildContext</span> context) {
    <span class="pl-k">return</span> <span class="pl-c1">TextFormField</span>(
      key<span class="pl-k">:</span> <span class="pl-c1">Page1</span>.value1Key,
    );
  }
}

<span class="pl-k">class</span> <span class="pl-c1">Page2</span> <span class="pl-k">extends</span> <span class="pl-c1">StatefulWidget</span> {

  <span class="pl-k">static</span> <span class="pl-k">final</span> <span class="pl-c1">GlobalKey</span>&lt;<span class="pl-c1">FormFieldState</span>&lt;<span class="pl-c1">String</span>&gt;&gt; value2Key <span class="pl-k">=</span> <span class="pl-c1">GlobalKey</span>&lt;<span class="pl-c1">FormFieldState</span>&lt;<span class="pl-c1">String</span>&gt;&gt;();

  <span class="pl-k">@override</span>
  <span class="pl-c1">_Page2State</span> <span class="pl-en">createState</span>() <span class="pl-k">=&gt;</span> <span class="pl-k">new</span> <span class="pl-c1">_Page2State</span>();
}

<span class="pl-k">class</span> <span class="pl-c1">_Page2State</span> <span class="pl-k">extends</span> <span class="pl-c1">State</span>&lt;<span class="pl-c1">Page2</span>&gt; <span class="pl-k">with</span> <span class="pl-c1">AutomaticKeepAliveClientMixin</span> {
  <span class="pl-k">@override</span>
  <span class="pl-c1">bool</span> <span class="pl-k">get</span> wantKeepAlive <span class="pl-k">=&gt;</span> <span class="pl-c1">true</span>;

  <span class="pl-k">@override</span>
  <span class="pl-c1">Widget</span> <span class="pl-en">build</span>(<span class="pl-c1">BuildContext</span> context) {
    <span class="pl-k">return</span> <span class="pl-c1">TextFormField</span>(
      key<span class="pl-k">:</span> <span class="pl-c1">Page2</span>.value2Key,
    );
  }
}

<span class="pl-k">class</span> <span class="pl-c1">Page3</span> <span class="pl-k">extends</span> <span class="pl-c1">StatefulWidget</span> {

  <span class="pl-k">static</span> <span class="pl-k">final</span> <span class="pl-c1">GlobalKey</span>&lt;<span class="pl-c1">FormFieldState</span>&lt;<span class="pl-c1">String</span>&gt;&gt; value3Key <span class="pl-k">=</span> <span class="pl-c1">GlobalKey</span>&lt;<span class="pl-c1">FormFieldState</span>&lt;<span class="pl-c1">String</span>&gt;&gt;();

  <span class="pl-k">@override</span>
  <span class="pl-c1">_Page3State</span> <span class="pl-en">createState</span>() <span class="pl-k">=&gt;</span> <span class="pl-k">new</span> <span class="pl-c1">_Page3State</span>();
}

<span class="pl-k">class</span> <span class="pl-c1">_Page3State</span> <span class="pl-k">extends</span> <span class="pl-c1">State</span>&lt;<span class="pl-c1">Page3</span>&gt; <span class="pl-k">with</span> <span class="pl-c1">AutomaticKeepAliveClientMixin</span> {
  <span class="pl-k">@override</span>
  <span class="pl-c1">bool</span> <span class="pl-k">get</span> wantKeepAlive <span class="pl-k">=&gt;</span> <span class="pl-c1">true</span>;

  <span class="pl-k">@override</span>
  <span class="pl-c1">Widget</span> <span class="pl-en">build</span>(<span class="pl-c1">BuildContext</span> context) {
    <span class="pl-k">return</span> <span class="pl-c1">TextFormField</span>(
      key<span class="pl-k">:</span> <span class="pl-c1">Page3</span>.value3Key,
    );
  }
}</pre></div>
<h2 dir="auto">Logs</h2>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="I/flutter ( 4547): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter ( 4547): The following assertion was thrown while finalizing the widget tree:
I/flutter ( 4547): Duplicate GlobalKey detected in widget tree.
I/flutter ( 4547): The following GlobalKey was specified multiple times in the widget tree. This will lead to parts of
I/flutter ( 4547): the widget tree being truncated unexpectedly, because the second time a key is seen, the previous
I/flutter ( 4547): instance is moved to the new location. The key was:
I/flutter ( 4547): - [LabeledGlobalKey&lt;FormFieldState&lt;String&gt;&gt;#742f4]
I/flutter ( 4547): This was determined by noticing that after the widget with the above global key was moved out of its
I/flutter ( 4547): respective previous parents, those previous parents never updated during this frame, meaning that
I/flutter ( 4547): they either did not update at all or updated before the widget was moved, in either case implying
I/flutter ( 4547): that they still think that they should have a child with that global key.
I/flutter ( 4547): The specific parents that did not update after having one or more children forcibly removed due to
I/flutter ( 4547): GlobalKey reparenting are:
I/flutter ( 4547): - Padding(padding: EdgeInsets(12.0, 0.0, 12.0, 0.0), renderObject: RenderPadding#86551 NEEDS-LAYOUT
I/flutter ( 4547):   DETACHED)
I/flutter ( 4547):   Page1(state: _Page1State#aa8d1)
I/flutter ( 4547):   Padding(padding: EdgeInsets(12.0, 0.0, 12.0, 0.0), renderObject: RenderPadding#0adeb NEEDS-LAYOUT
I/flutter ( 4547):   DETACHED)
I/flutter ( 4547): A GlobalKey can only be specified on one widget at a time in the widget tree.
I/flutter ( 4547): 
I/flutter ( 4547): When the exception was thrown, this was the stack:
I/flutter ( 4547): #0      BuildOwner.finalizeTree.&lt;anonymous closure&gt; (package:flutter/src/widgets/framework.dart:2386:15)
I/flutter ( 4547): #1      BuildOwner.finalizeTree (package:flutter/src/widgets/framework.dart:2407:8)
I/flutter ( 4547): #2      _WidgetsFlutterBinding&amp;BindingBase&amp;GestureBinding&amp;ServicesBinding&amp;SchedulerBinding&amp;PaintingBinding&amp;RendererBinding&amp;WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:628:18)
I/flutter ( 4547): #3      _WidgetsFlutterBinding&amp;BindingBase&amp;GestureBinding&amp;ServicesBinding&amp;SchedulerBinding&amp;PaintingBinding&amp;RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:208:5)
I/flutter ( 4547): #4      _WidgetsFlutterBinding&amp;BindingBase&amp;GestureBinding&amp;ServicesBinding&amp;SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:990:15)
I/flutter ( 4547): #5      _WidgetsFlutterBinding&amp;BindingBase&amp;GestureBinding&amp;ServicesBinding&amp;SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:930:9)
I/flutter ( 4547): #6      _WidgetsFlutterBinding&amp;BindingBase&amp;GestureBinding&amp;ServicesBinding&amp;SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:842:5)
I/flutter ( 4547): #7      _invoke (dart:ui/hooks.dart:120:13)
I/flutter ( 4547): #8      _drawFrame (dart:ui/hooks.dart:109:3)
I/flutter ( 4547): ════════════════════════════════════════════════════════════════════════════════════════════════════"><pre class="notranslate"><code class="notranslate">I/flutter ( 4547): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter ( 4547): The following assertion was thrown while finalizing the widget tree:
I/flutter ( 4547): Duplicate GlobalKey detected in widget tree.
I/flutter ( 4547): The following GlobalKey was specified multiple times in the widget tree. This will lead to parts of
I/flutter ( 4547): the widget tree being truncated unexpectedly, because the second time a key is seen, the previous
I/flutter ( 4547): instance is moved to the new location. The key was:
I/flutter ( 4547): - [LabeledGlobalKey&lt;FormFieldState&lt;String&gt;&gt;#742f4]
I/flutter ( 4547): This was determined by noticing that after the widget with the above global key was moved out of its
I/flutter ( 4547): respective previous parents, those previous parents never updated during this frame, meaning that
I/flutter ( 4547): they either did not update at all or updated before the widget was moved, in either case implying
I/flutter ( 4547): that they still think that they should have a child with that global key.
I/flutter ( 4547): The specific parents that did not update after having one or more children forcibly removed due to
I/flutter ( 4547): GlobalKey reparenting are:
I/flutter ( 4547): - Padding(padding: EdgeInsets(12.0, 0.0, 12.0, 0.0), renderObject: RenderPadding#86551 NEEDS-LAYOUT
I/flutter ( 4547):   DETACHED)
I/flutter ( 4547):   Page1(state: _Page1State#aa8d1)
I/flutter ( 4547):   Padding(padding: EdgeInsets(12.0, 0.0, 12.0, 0.0), renderObject: RenderPadding#0adeb NEEDS-LAYOUT
I/flutter ( 4547):   DETACHED)
I/flutter ( 4547): A GlobalKey can only be specified on one widget at a time in the widget tree.
I/flutter ( 4547): 
I/flutter ( 4547): When the exception was thrown, this was the stack:
I/flutter ( 4547): #0      BuildOwner.finalizeTree.&lt;anonymous closure&gt; (package:flutter/src/widgets/framework.dart:2386:15)
I/flutter ( 4547): #1      BuildOwner.finalizeTree (package:flutter/src/widgets/framework.dart:2407:8)
I/flutter ( 4547): #2      _WidgetsFlutterBinding&amp;BindingBase&amp;GestureBinding&amp;ServicesBinding&amp;SchedulerBinding&amp;PaintingBinding&amp;RendererBinding&amp;WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:628:18)
I/flutter ( 4547): #3      _WidgetsFlutterBinding&amp;BindingBase&amp;GestureBinding&amp;ServicesBinding&amp;SchedulerBinding&amp;PaintingBinding&amp;RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:208:5)
I/flutter ( 4547): #4      _WidgetsFlutterBinding&amp;BindingBase&amp;GestureBinding&amp;ServicesBinding&amp;SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:990:15)
I/flutter ( 4547): #5      _WidgetsFlutterBinding&amp;BindingBase&amp;GestureBinding&amp;ServicesBinding&amp;SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:930:9)
I/flutter ( 4547): #6      _WidgetsFlutterBinding&amp;BindingBase&amp;GestureBinding&amp;ServicesBinding&amp;SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:842:5)
I/flutter ( 4547): #7      _invoke (dart:ui/hooks.dart:120:13)
I/flutter ( 4547): #8      _drawFrame (dart:ui/hooks.dart:109:3)
I/flutter ( 4547): ════════════════════════════════════════════════════════════════════════════════════════════════════
</code></pre></div>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="[√] Flutter (Channel dev, v0.5.1, on Microsoft Windows [Version 10.0.16299.431], locale en-US)
    • Flutter version 0.5.1 at C:\Users\hillel\Documents\flutter
    • Framework revision c7ea3ca377 (13 days ago), 2018-05-29 21:07:33 +0200
    • Engine revision 1ed25ca7b7
    • Dart version 2.0.0-dev.58.0.flutter-f981f09760

[√] Android toolchain - develop for Android devices (Android SDK 27.0.3)
    • Android SDK at C:\Users\hillel\AppData\Local\Android\sdk
    • Android NDK location not configured (optional; useful for native profiling support)
    • Platform android-27, build-tools 27.0.3
    • Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
    • Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1024-b02)
    • All Android licenses accepted.

[√] Android Studio (version 3.1)
    • Android Studio at C:\Program Files\Android\Android Studio
    • Flutter plugin version 24.2.1
    • Dart plugin version 173.4700
    • Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1024-b02)

[√] Connected devices (1 available)
    • Android SDK built for x86 64 • emulator-5554 • android-x64 • Android P (API 27) (emulator)

• No issues found!"><pre class="notranslate"><code class="notranslate">[√] Flutter (Channel dev, v0.5.1, on Microsoft Windows [Version 10.0.16299.431], locale en-US)
    • Flutter version 0.5.1 at C:\Users\hillel\Documents\flutter
    • Framework revision c7ea3ca377 (13 days ago), 2018-05-29 21:07:33 +0200
    • Engine revision 1ed25ca7b7
    • Dart version 2.0.0-dev.58.0.flutter-f981f09760

[√] Android toolchain - develop for Android devices (Android SDK 27.0.3)
    • Android SDK at C:\Users\hillel\AppData\Local\Android\sdk
    • Android NDK location not configured (optional; useful for native profiling support)
    • Platform android-27, build-tools 27.0.3
    • Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
    • Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1024-b02)
    • All Android licenses accepted.

[√] Android Studio (version 3.1)
    • Android Studio at C:\Program Files\Android\Android Studio
    • Flutter plugin version 24.2.1
    • Dart plugin version 173.4700
    • Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1024-b02)

[√] Connected devices (1 available)
    • Android SDK built for x86 64 • emulator-5554 • android-x64 • Android P (API 27) (emulator)

• No issues found!
</code></pre></div>
<p dir="auto">Thanks for your help! Hope it's actually a bug and not user error...</p>
<h2 dir="auto">Steps to Reproduce</h2>
<p dir="auto">I have a PageView that contains the top level widgets for my app, with switching between them controlled by a BottomNavBar. As per <a class="user-mention notranslate" data-hovercard-type="user" data-hovercard-url="/users/Hixie/hovercard" data-octo-click="hovercard-link-click" data-octo-dimensions="link_type:self" href="https://github.com/Hixie">@Hixie</a>'s advice in the chat, I am adding <code class="notranslate">AutomaticKeepAliveClientMixin</code> to these top level widgets so the PageView won't recycle them and will preserve state. After I added this to the main widget that contains a network loaded ListView, on occasion when switching back to this ListView from another tab I get this failed assertion in the framework.</p>
<h2 dir="auto">Logs</h2>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
The following assertion was thrown building NotificationListener&lt;KeepAliveNotification&gt;:
'package:flutter/src/rendering/object.dart': Failed assertion: line 3031 pos 14:
'_debugUltimatePreviousSiblingOf(after, equals: _firstChild)': is not true.
Either the assertion indicates an error in the framework itself, or we should provide substantially
more information in this error message to help you determine and fix the underlying cause.
In either case, please report this assertion by filing a bug on GitHub:
  https://github.com/flutter/flutter/issues/new
When the exception was thrown, this was the stack:
#2      RenderSliver&amp;ContainerRenderObjectMixin._insertIntoChildList (package:flutter/src/rendering/object.dart:3031:14)
#3      RenderSliver&amp;ContainerRenderObjectMixin.insert (package:flutter/src/rendering/object.dart:3065:5)
#4      RenderSliverMultiBoxAdaptor.insert (package:flutter/src/rendering/sliver_multi_box_adaptor.dart:193:17)
#5      SliverMultiBoxAdaptorElement.insertChildRenderObject (package:flutter/src/widgets/sliver.dart:840:18)
#6      RenderObjectElement.attachRenderObject (package:flutter/src/widgets/framework.dart:4380:35)
#7      RenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4151:5)
#8      SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4515:16)
#9      Element.inflateWidget (package:flutter/src/widgets/framework.dart:2882:14)
#10     Element.updateChild (package:flutter/src/widgets/framework.dart:2685:12)
#11     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#12     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#13     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3514:5)
#14     ComponentElement.mount (package:flutter/src/widgets/framework.dart:3509:5)
#15     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2882:14)
#16     Element.updateChild (package:flutter/src/widgets/framework.dart:2685:12)
#17     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#18     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#19     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3514:5)
#20     ComponentElement.mount (package:flutter/src/widgets/framework.dart:3509:5)
#21     ParentDataElement.mount (package:flutter/src/widgets/framework.dart:3827:16)
#22     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2882:14)
#23     Element.updateChild (package:flutter/src/widgets/framework.dart:2685:12)
#24     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#25     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#26     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3514:5)
#27     StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3652:22)
#28     ComponentElement.mount (package:flutter/src/widgets/framework.dart:3509:5)
#29     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2882:14)
#30     Element.updateChild (package:flutter/src/widgets/framework.dart:2685:12)
#31     SliverMultiBoxAdaptorElement.performRebuild (package:flutter/src/widgets/sliver.dart:696:34)
#32     SliverMultiBoxAdaptorElement.update (package:flutter/src/widgets/sliver.dart:665:7)
#33     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#34     RenderObjectElement.updateChildren (package:flutter/src/widgets/framework.dart:4250:32)
#35     MultiChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4631:17)
#36     _ViewportElement.update (package:flutter/src/widgets/viewport.dart:150:17)
#37     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#38     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#39     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#40     ProxyElement.update (package:flutter/src/widgets/framework.dart:3781:5)
#41     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#42     SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4523:14)
#43     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#44     SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4523:14)
#45     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#46     SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4523:14)
#47     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#48     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#49     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#50     StatefulElement.update (package:flutter/src/widgets/framework.dart:3671:5)
#51     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#52     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#53     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#54     StatefulElement.update (package:flutter/src/widgets/framework.dart:3671:5)
#55     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#56     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#57     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#58     StatelessElement.update (package:flutter/src/widgets/framework.dart:3596:5)
#59     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#60     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#61     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#62     StatefulElement.update (package:flutter/src/widgets/framework.dart:3671:5)
#63     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#64     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#65     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#66     ProxyElement.update (package:flutter/src/widgets/framework.dart:3781:5)
#67     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#68     RenderObjectElement.updateChildren (package:flutter/src/widgets/framework.dart:4250:32)
#69     MultiChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4631:17)
#70     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#71     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#72     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#73     ProxyElement.update (package:flutter/src/widgets/framework.dart:3781:5)
#74     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#75     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#76     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#77     StatefulElement.update (package:flutter/src/widgets/framework.dart:3671:5)
#78     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#79     SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4523:14)
#80     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#81     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#82     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#83     StatelessElement.update (package:flutter/src/widgets/framework.dart:3596:5)
#84     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#85     SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4523:14)
#86     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#87     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#88     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#89     StatefulElement.update (package:flutter/src/widgets/framework.dart:3671:5)
#90     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#91     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#92     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#93     StatefulElement.update (package:flutter/src/widgets/framework.dart:3671:5)
#94     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#95     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#96     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#97     ProxyElement.update (package:flutter/src/widgets/framework.dart:3781:5)
#98     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#99     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#100    Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#101    ProxyElement.update (package:flutter/src/widgets/framework.dart:3781:5)
#102    Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#103    ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#104    Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#105    StatefulElement.update (package:flutter/src/widgets/framework.dart:3671:5)
#106    Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#107    ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#108    Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#109    BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2260:33)
#110    BindingBase&amp;SchedulerBinding&amp;GestureBinding&amp;ServicesBinding&amp;RendererBinding&amp;WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:503:20)
#111    BindingBase&amp;SchedulerBinding&amp;GestureBinding&amp;ServicesBinding&amp;RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:189:5)
#112    BindingBase&amp;SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:695:15)
#113    BindingBase&amp;SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:643:9)
#114    _invoke (file:///b/build/slave/Mac_Engine/build/src/flutter/lib/ui/hooks.dart:86)
#115    _drawFrame (file:///b/build/slave/Mac_Engine/build/src/flutter/lib/ui/hooks.dart:75)
(elided 2 frames from class _AssertionError)
════════════════════════════════════════════════════════════════════════════════════════════════════
Another exception was thrown: 'package:flutter/src/rendering/object.dart': Failed assertion: line 3031 pos 14: '_debugUltimatePreviousSiblingOf(after, equals: _firstChild)': is not true.
Another exception was thrown: 'package:flutter/src/rendering/object.dart': Failed assertion: line 3031 pos 14: '_debugUltimatePreviousSiblingOf(after, equals: _firstChild)': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true."><pre class="notranslate"><code class="notranslate">══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
The following assertion was thrown building NotificationListener&lt;KeepAliveNotification&gt;:
'package:flutter/src/rendering/object.dart': Failed assertion: line 3031 pos 14:
'_debugUltimatePreviousSiblingOf(after, equals: _firstChild)': is not true.
Either the assertion indicates an error in the framework itself, or we should provide substantially
more information in this error message to help you determine and fix the underlying cause.
In either case, please report this assertion by filing a bug on GitHub:
  https://github.com/flutter/flutter/issues/new
When the exception was thrown, this was the stack:
#2      RenderSliver&amp;ContainerRenderObjectMixin._insertIntoChildList (package:flutter/src/rendering/object.dart:3031:14)
#3      RenderSliver&amp;ContainerRenderObjectMixin.insert (package:flutter/src/rendering/object.dart:3065:5)
#4      RenderSliverMultiBoxAdaptor.insert (package:flutter/src/rendering/sliver_multi_box_adaptor.dart:193:17)
#5      SliverMultiBoxAdaptorElement.insertChildRenderObject (package:flutter/src/widgets/sliver.dart:840:18)
#6      RenderObjectElement.attachRenderObject (package:flutter/src/widgets/framework.dart:4380:35)
#7      RenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4151:5)
#8      SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4515:16)
#9      Element.inflateWidget (package:flutter/src/widgets/framework.dart:2882:14)
#10     Element.updateChild (package:flutter/src/widgets/framework.dart:2685:12)
#11     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#12     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#13     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3514:5)
#14     ComponentElement.mount (package:flutter/src/widgets/framework.dart:3509:5)
#15     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2882:14)
#16     Element.updateChild (package:flutter/src/widgets/framework.dart:2685:12)
#17     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#18     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#19     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3514:5)
#20     ComponentElement.mount (package:flutter/src/widgets/framework.dart:3509:5)
#21     ParentDataElement.mount (package:flutter/src/widgets/framework.dart:3827:16)
#22     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2882:14)
#23     Element.updateChild (package:flutter/src/widgets/framework.dart:2685:12)
#24     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#25     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#26     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3514:5)
#27     StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3652:22)
#28     ComponentElement.mount (package:flutter/src/widgets/framework.dart:3509:5)
#29     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2882:14)
#30     Element.updateChild (package:flutter/src/widgets/framework.dart:2685:12)
#31     SliverMultiBoxAdaptorElement.performRebuild (package:flutter/src/widgets/sliver.dart:696:34)
#32     SliverMultiBoxAdaptorElement.update (package:flutter/src/widgets/sliver.dart:665:7)
#33     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#34     RenderObjectElement.updateChildren (package:flutter/src/widgets/framework.dart:4250:32)
#35     MultiChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4631:17)
#36     _ViewportElement.update (package:flutter/src/widgets/viewport.dart:150:17)
#37     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#38     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#39     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#40     ProxyElement.update (package:flutter/src/widgets/framework.dart:3781:5)
#41     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#42     SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4523:14)
#43     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#44     SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4523:14)
#45     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#46     SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4523:14)
#47     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#48     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#49     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#50     StatefulElement.update (package:flutter/src/widgets/framework.dart:3671:5)
#51     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#52     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#53     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#54     StatefulElement.update (package:flutter/src/widgets/framework.dart:3671:5)
#55     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#56     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#57     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#58     StatelessElement.update (package:flutter/src/widgets/framework.dart:3596:5)
#59     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#60     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#61     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#62     StatefulElement.update (package:flutter/src/widgets/framework.dart:3671:5)
#63     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#64     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#65     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#66     ProxyElement.update (package:flutter/src/widgets/framework.dart:3781:5)
#67     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#68     RenderObjectElement.updateChildren (package:flutter/src/widgets/framework.dart:4250:32)
#69     MultiChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4631:17)
#70     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#71     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#72     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#73     ProxyElement.update (package:flutter/src/widgets/framework.dart:3781:5)
#74     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#75     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#76     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#77     StatefulElement.update (package:flutter/src/widgets/framework.dart:3671:5)
#78     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#79     SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4523:14)
#80     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#81     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#82     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#83     StatelessElement.update (package:flutter/src/widgets/framework.dart:3596:5)
#84     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#85     SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:4523:14)
#86     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#87     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#88     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#89     StatefulElement.update (package:flutter/src/widgets/framework.dart:3671:5)
#90     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#91     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#92     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#93     StatefulElement.update (package:flutter/src/widgets/framework.dart:3671:5)
#94     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#95     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#96     Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#97     ProxyElement.update (package:flutter/src/widgets/framework.dart:3781:5)
#98     Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#99     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#100    Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#101    ProxyElement.update (package:flutter/src/widgets/framework.dart:3781:5)
#102    Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#103    ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#104    Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#105    StatefulElement.update (package:flutter/src/widgets/framework.dart:3671:5)
#106    Element.updateChild (package:flutter/src/widgets/framework.dart:2674:15)
#107    ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3546:16)
#108    Element.rebuild (package:flutter/src/widgets/framework.dart:3435:5)
#109    BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2260:33)
#110    BindingBase&amp;SchedulerBinding&amp;GestureBinding&amp;ServicesBinding&amp;RendererBinding&amp;WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:503:20)
#111    BindingBase&amp;SchedulerBinding&amp;GestureBinding&amp;ServicesBinding&amp;RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:189:5)
#112    BindingBase&amp;SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:695:15)
#113    BindingBase&amp;SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:643:9)
#114    _invoke (file:///b/build/slave/Mac_Engine/build/src/flutter/lib/ui/hooks.dart:86)
#115    _drawFrame (file:///b/build/slave/Mac_Engine/build/src/flutter/lib/ui/hooks.dart:75)
(elided 2 frames from class _AssertionError)
════════════════════════════════════════════════════════════════════════════════════════════════════
Another exception was thrown: 'package:flutter/src/rendering/object.dart': Failed assertion: line 3031 pos 14: '_debugUltimatePreviousSiblingOf(after, equals: _firstChild)': is not true.
Another exception was thrown: 'package:flutter/src/rendering/object.dart': Failed assertion: line 3031 pos 14: '_debugUltimatePreviousSiblingOf(after, equals: _firstChild)': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
Another exception was thrown: 'package:flutter/src/widgets/framework.dart': Failed assertion: line 3437 pos 14: 'owner._debugCurrentBuildTarget == this': is not true.
</code></pre></div>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="Analyzing /Users/matt/code/flutter/kudos...
  lint • Don't import implementation files from another package at lib/feed.dart:5:8 • implementation_imports
  lint • Close instances of `dart.core.Sink` at lib/feed.dart:26:26 • close_sinks
  lint • Don't explicitly initialize variables to null at lib/loading_list_view.dart:23:5 • avoid_init_to_null
  lint • Don't import implementation files from another package at lib/post.dart:3:8 • implementation_imports
  hint • Unused import at lib/application.dart:4:8 • unused_import
  hint • Unused import at lib/feed.dart:2:8 • unused_import
  hint • Unused import at lib/feed.dart:5:8 • unused_import
  hint • Unused import at lib/feed.dart:7:8 • unused_import
  hint • Unused import at lib/feed.dart:12:8 • unused_import
  hint • Unused import at lib/feed.dart:13:8 • unused_import
  hint • This method overrides a method annotated as @mustCallSuper in 'State', but does not invoke the overridden method at lib/feed.dart:29:8 • must_call_super
  hint • This method overrides a method annotated as @mustCallSuper in 'State', but does not invoke the overridden method at lib/feed.dart:40:8 • must_call_super
  hint • The type parameter 'widgetAdapter' is annotated with @required but only named parameters without default value can be annotated with it at lib/loading_list_view.dart:23:5 • invalid_required_param
  hint • Unused import at lib/main.dart:6:8 • unused_import
  hint • The value of the field '_counter' isn't used at lib/main.dart:56:7 • unused_field
  hint • This method overrides a method annotated as @mustCallSuper in 'State', but does not invoke the overridden method at lib/main.dart:63:8 • must_call_super
  hint • This method overrides a method annotated as @mustCallSuper in 'State', but does not invoke the overridden method at lib/main.dart:71:8 • must_call_super
  hint • The method '_incrementCounter' isn't used at lib/main.dart:76:8 • unused_element
  hint • Unused import at lib/post.dart:7:8 • unused_import
  hint • This class inherits from a class marked as @immutable, and therefore should be immutable (all instance fields must be final) at lib/post.dart:10:7 • must_be_immutable
  hint • This class inherits from a class marked as @immutable, and therefore should be immutable (all instance fields must be final) at lib/post.dart:34:7 • must_be_immutable
  hint • The value of the local variable 'plainText' isn't used at lib/post.dart:71:10 • unused_local_variable
  hint • This class inherits from a class marked as @immutable, and therefore should be immutable (all instance fields must be final) at lib/post.dart:112:7 • must_be_immutable
  hint • This class inherits from a class marked as @immutable, and therefore should be immutable (all instance fields must be final) at lib/post.dart:160:7 • must_be_immutable
  hint • This class inherits from a class marked as @immutable, and therefore should be immutable (all instance fields must be final) at lib/profile.dart:10:7 • must_be_immutable
  hint • This method overrides a method annotated as @mustCallSuper in 'State', but does not invoke the overridden method at lib/profile.dart:27:10 • must_call_super
  hint • This class inherits from a class marked as @immutable, and therefore should be immutable (all instance fields must be final) at lib/profile.dart:145:7 • must_be_immutable
  hint • The class '_KudosEarned' isn't used at lib/profile.dart:218:7 • unused_element
  hint • Unused import at lib/send_photo.dart:5:8 • unused_import
  hint • Unused import at lib/usersearch.dart:6:8 • unused_import
  hint • Unused import at lib/usersearch.dart:7:8 • unused_import
  hint • This method overrides a method annotated as @mustCallSuper in 'State', but does not invoke the overridden method at lib/usersearch.dart:25:10 • must_call_super
32 issues found."><pre class="notranslate"><code class="notranslate">Analyzing /Users/matt/code/flutter/kudos...
  lint • Don't import implementation files from another package at lib/feed.dart:5:8 • implementation_imports
  lint • Close instances of `dart.core.Sink` at lib/feed.dart:26:26 • close_sinks
  lint • Don't explicitly initialize variables to null at lib/loading_list_view.dart:23:5 • avoid_init_to_null
  lint • Don't import implementation files from another package at lib/post.dart:3:8 • implementation_imports
  hint • Unused import at lib/application.dart:4:8 • unused_import
  hint • Unused import at lib/feed.dart:2:8 • unused_import
  hint • Unused import at lib/feed.dart:5:8 • unused_import
  hint • Unused import at lib/feed.dart:7:8 • unused_import
  hint • Unused import at lib/feed.dart:12:8 • unused_import
  hint • Unused import at lib/feed.dart:13:8 • unused_import
  hint • This method overrides a method annotated as @mustCallSuper in 'State', but does not invoke the overridden method at lib/feed.dart:29:8 • must_call_super
  hint • This method overrides a method annotated as @mustCallSuper in 'State', but does not invoke the overridden method at lib/feed.dart:40:8 • must_call_super
  hint • The type parameter 'widgetAdapter' is annotated with @required but only named parameters without default value can be annotated with it at lib/loading_list_view.dart:23:5 • invalid_required_param
  hint • Unused import at lib/main.dart:6:8 • unused_import
  hint • The value of the field '_counter' isn't used at lib/main.dart:56:7 • unused_field
  hint • This method overrides a method annotated as @mustCallSuper in 'State', but does not invoke the overridden method at lib/main.dart:63:8 • must_call_super
  hint • This method overrides a method annotated as @mustCallSuper in 'State', but does not invoke the overridden method at lib/main.dart:71:8 • must_call_super
  hint • The method '_incrementCounter' isn't used at lib/main.dart:76:8 • unused_element
  hint • Unused import at lib/post.dart:7:8 • unused_import
  hint • This class inherits from a class marked as @immutable, and therefore should be immutable (all instance fields must be final) at lib/post.dart:10:7 • must_be_immutable
  hint • This class inherits from a class marked as @immutable, and therefore should be immutable (all instance fields must be final) at lib/post.dart:34:7 • must_be_immutable
  hint • The value of the local variable 'plainText' isn't used at lib/post.dart:71:10 • unused_local_variable
  hint • This class inherits from a class marked as @immutable, and therefore should be immutable (all instance fields must be final) at lib/post.dart:112:7 • must_be_immutable
  hint • This class inherits from a class marked as @immutable, and therefore should be immutable (all instance fields must be final) at lib/post.dart:160:7 • must_be_immutable
  hint • This class inherits from a class marked as @immutable, and therefore should be immutable (all instance fields must be final) at lib/profile.dart:10:7 • must_be_immutable
  hint • This method overrides a method annotated as @mustCallSuper in 'State', but does not invoke the overridden method at lib/profile.dart:27:10 • must_call_super
  hint • This class inherits from a class marked as @immutable, and therefore should be immutable (all instance fields must be final) at lib/profile.dart:145:7 • must_be_immutable
  hint • The class '_KudosEarned' isn't used at lib/profile.dart:218:7 • unused_element
  hint • Unused import at lib/send_photo.dart:5:8 • unused_import
  hint • Unused import at lib/usersearch.dart:6:8 • unused_import
  hint • Unused import at lib/usersearch.dart:7:8 • unused_import
  hint • This method overrides a method annotated as @mustCallSuper in 'State', but does not invoke the overridden method at lib/usersearch.dart:25:10 • must_call_super
32 issues found.
</code></pre></div>
<h2 dir="auto">Flutter Doctor</h2>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="[✓] Flutter (on Mac OS X 10.12.6 16G29, locale en-US, channel alpha)
    • Flutter at /Users/matt/code/flutter/flutter
    • Framework revision b156a0f054 (3 weeks ago), 2017-08-11 22:01:40 -0700
    • Engine revision fef7d827d6
    • Tools Dart version 1.25.0-dev.9.0

[✓] Android toolchain - develop for Android devices (Android SDK 25.0.3)
    • Android SDK at /Users/matt/code/android/android
    • Platform android-25, build-tools 25.0.3
    • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_112-release-b06)

[✓] iOS toolchain - develop for iOS devices (Xcode 8.3.3)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 8.3.3, Build version 8E3004b
    • ios-deploy 1.9.1
    • CocoaPods version 1.3.1

[✓] Android Studio (version 2.3)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Java version OpenJDK Runtime Environment (build 1.8.0_112-release-b06)

[✓] IntelliJ IDEA Ultimate Edition (version 2017.2.2)
    • Flutter plugin version 16.0
    • Dart plugin version 172.3757.55

[✓] Connected devices
    • iPhone 6s • 3DF999CB-1CD6-4649-8187-DDEFBDB14DFA • ios • iOS 10.3 (simulator)
"><pre class="notranslate"><code class="notranslate">[✓] Flutter (on Mac OS X 10.12.6 16G29, locale en-US, channel alpha)
    • Flutter at /Users/matt/code/flutter/flutter
    • Framework revision b156a0f054 (3 weeks ago), 2017-08-11 22:01:40 -0700
    • Engine revision fef7d827d6
    • Tools Dart version 1.25.0-dev.9.0

[✓] Android toolchain - develop for Android devices (Android SDK 25.0.3)
    • Android SDK at /Users/matt/code/android/android
    • Platform android-25, build-tools 25.0.3
    • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_112-release-b06)

[✓] iOS toolchain - develop for iOS devices (Xcode 8.3.3)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 8.3.3, Build version 8E3004b
    • ios-deploy 1.9.1
    • CocoaPods version 1.3.1

[✓] Android Studio (version 2.3)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Java version OpenJDK Runtime Environment (build 1.8.0_112-release-b06)

[✓] IntelliJ IDEA Ultimate Edition (version 2017.2.2)
    • Flutter plugin version 16.0
    • Dart plugin version 172.3757.55

[✓] Connected devices
    • iPhone 6s • 3DF999CB-1CD6-4649-8187-DDEFBDB14DFA • ios • iOS 10.3 (simulator)

</code></pre></div>
<blockquote>
<p dir="auto">For more information about diagnosing and reporting Flutter bugs, please see <a href="https://flutter.io/bug-reports/" rel="nofollow">https://flutter.io/bug-reports/</a>.</p>
</blockquote>