Flutter Http call List<t> always result Null in UI - flutter

Question

I have try many sample in stack but still can`t get the idea which part i miss, the result in UI always display null, ..
here is the code i try :
class PointBallance {
String id, date, datetime, companyid, storecode, customercode, topup, amount, remark, cashier, invoice ;
PointBallance({this.id, this.date, this.datetime, this.companyid, this.storecode, this.customercode, this.topup, this.amount, this.remark, this.cashier, this.invoice});
factory PointBallance.fromJson(Map<String, dynamic> json) {
return PointBallance(
id: json['id'],
date: json['date'],
datetime: json['datetime'],
companyid: json['company_id'],
storecode: json['store_code'],
customercode: json['customer_code'],
topup: json['topup'],
amount: json['amount'],
remark: json['remark'],
cashier: json['cashier'],
invoice: json['invoice'],
);
}
}
the part for call http is here :
Future<List<PointBallance>> pointBal() async {
var url = 'http://someUrl';
var res = await http.get(url);
if(res.statusCode == 200) {
var dtpoint = json.decode(res.body);
print(dtpoint);
var bel = List<PointBallance>.from(dtpoint.map((i) => PointBallance.fromJson(i)));
return bel;
} else {
throw Exception(
"Request to $url failed with status ${res.statusCode}: ${res.body}"
);
}
}
and for screen to display data ..
class _PointScreenState extends State<PointScreen> {
Future<List<PointBallance>> _point;
AuthService _authService = new AuthService();
#override
void initState() {
_point = _authService.pointBal();
super.initState();
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('My Point'),
),
body: FutureBuilder<List<PointBallance>>(
future: _point,
builder: (context, snapshot) {
if (snapshot.hasData) {
var dt = snapshot.data[0].id;
return Column(
children: <Widget>[
**Text('in the top $dt'),**
Expanded(
child: ListView.builder(
itemCount: snapshot.data.length,
itemBuilder:(BuildContext context, int index){
var hei = snapshot.data[index];
return **Text(hei.id != null ? hei.id : 'Cant get data')**;
}),
),
],
);
} else if (snapshot.hasError) {
return Text('${snapshot.error}');
}
return CircularProgressIndicator();
}),
);
}
}
in console i got result
print(dtpoint);
any guide to correctly display data result? because in console there is result.