How to return a widget if it is the last index of a list?

i want to retun a widget if it is the last item in the method but i get an error ... Tried calling: call()

 itemList.last()
     ? CircleAvatar(
       backgroundColor: mainColor,
       radius: 15,
       child: Icon(Icons.done),
        )
      : Container()

assuming your are using a ListView.builder()

class _MyAppState extends State<MyApp> {
  @override
  Widget build(BuildContext context) {
    List<String> item = [
      'jan',
      'feb',
      'mar',
      'apr',
      'may',
      'jun',
      'jul',
      'aug',
      'sep',
      'oct',
      'nov',
      'dec'
    ];
    return Scaffold(
      body: ListView.builder(
        itemCount: item.length,
        itemBuilder: (context, index) {
          if (index == item.length - 1) {
            return ListTile(
              leading: Text('Last index reached'),
            );
          }
          return ListTile(
            leading: Text(item[index]),
          );
        },
      ),
    );
  }
}