throws exception when adding/removing tabs mid-animation

dynamic_tabs.dart

// Flutter code sample for material.TabController.2

// A sample application dynamically adds and removes tabs.

import 'dart:math' as math;
import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyTabbedPage(title: 'Dynamic tabs demo'),
    );
  }
}

class MyTabbedPage extends StatefulWidget {
  MyTabbedPage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyTabbedPageState createState() => _MyTabbedPageState();
}

class _MyTabbedPageState extends State<MyTabbedPage>
    with TickerProviderStateMixin {
  List<Tab> myTabs = <Tab>[
    Tab(text: '1'),
    Tab(text: '2'),
  ];

  TabController _tabController;

  @override
  void initState() {
    super.initState();
    _tabController = TabController(vsync: this, length: myTabs.length);
  }

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

  void _updateTabController() {
    int newIndex;
    if (_tabController.index >= myTabs.length) {
      newIndex = math.max(0, myTabs.length - 2);
    } else {
      newIndex = _tabController.index;
    }

    _tabController.dispose();
    _tabController = TabController(
      vsync: this,
      length: myTabs.length,
      initialIndex: newIndex,
    );
  }

  void _addNewTab() {
    setState(() {
      myTabs = myTabs.toList()
        ..add(Tab(text: '${myTabs.length + 1}'));
      _updateTabController();
    });
    setState((){});
  }

  void _removeLastTab() {
    setState(() {
      myTabs = myTabs.toList()
        ..removeLast();
      _updateTabController();
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
        actions: [
          IconButton(
            icon: Icon(Icons.remove),
            onPressed: _removeLastTab,
          ),
        ],
        bottom: TabBar(
          controller: _tabController,
          tabs: myTabs,
        ),
      ),
      body: TabBarView(
        controller: _tabController,
        children: myTabs.map((Tab tab) {
          final String label = tab.text.toLowerCase();
          return Center(
            child: Text(
              'This is the tab $label',
              style: const TextStyle(fontSize: 36),
            ),
          );
        }).toList(),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _addNewTab,
        child: Icon(Icons.add),
      ),
    );
  }
}