Range Error in listview.builders count

I tired to make a infinite scroll within listview.builder widgets. But it’s only show count : 10.

On Flutter App. I fetch the data from WordPress to Flutter using future aync and post show correctly. When i want to show the more the 10 post then error appear.

RangeError (index): Invalid value: Not in range 0…9, inclusive: 10

Take a look at screenshot.

My Code is :-

 ///scroller controller
  ScrollController _scrollController = ScrollController();

  int _currentMax = 12;

  ///drawer scafffold super key
//  final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();

  /// tab bar controller
  TabController _tabController;

  @override
  void initState() {
///tabbed
_tabController = new TabController(length: 11, vsync: this);

///post
this.getPosts();

//    /// Scroll controller
_scrollController.addListener(() {
  if (_scrollController.position.pixels ==
      _scrollController.position.maxScrollExtent) {
    _getMoreData();
  }
});

// fetchFive();
super.initState();
  }
  _getMoreData() {
for (int i = _currentMax; i < _currentMax + 12; i++) {
  this.getPosts();
}
_currentMax = _currentMax + 12;
setState(() {});
  }


Widget build(BuildContext context) {
final _recentpost = new RefreshIndicator(
  child: new ListView.builder(
    controller: _scrollController,  ///Scroll container
    itemCount: posts == null ? 0 : posts.length +1,
    itemBuilder: (BuildContext context, int index) {
      return Padding(
        padding: const EdgeInsets.only(top: 10.0, left: 2, right: 2),
        child: new Column(