ERROR : NoSuchMethodError: The method 'substring' was called on null - json

Question

I'm trying this certain app (world-time app) and constantly getting this error:
Used this HTTP Package for url:
import 'dart:convert';
import 'package:http/http.dart';
import 'package:intl/intl.dart';
class WorldTime {
String location;
String time;
String flag;
String url;
WorldTime({this.location, this.flag, this.url});
Future<void> getTime() async {
try {
Response response =
await get(Uri.https('worldtimeapi.org', 'api/timezone/$url'));
Map data = jsonDecode(response.body);
String datetime = data['datetime'];
String offset = data['utc_offset'].substring(1, 3);
DateTime now = DateTime.parse(datetime);
now = now.add(Duration(hours: int.parse(offset)));
time = DateFormat.jm().format(now);
} catch (e) {
print("Error occured: $e");
time = "Cannot Display Time Due to Error Occured";
}
}
}
imported world time api in this file:
import 'package:flutter/gestures.dart';
import 'package:flutter/material.dart';
import 'package:world_time_app/services/world_time.dart';
class loading extends StatefulWidget {
#override
_loadingState createState() => _loadingState();
}
class _loadingState extends State<loading> {
void setTime() async {
WorldTime instance =
WorldTime(location: 'Florida', flag: 'img.jpg', url: 'America/Florida');
await instance.getTime();
Navigator.pushReplacementNamed(context, '/home', arguments: {
'location' : instance.location,
'flag': instance.flag,
'time': instance.time,
});
}
#override
void initState() {
super.initState();
setTime();
}
#override
Widget build(BuildContext context) {
return Scaffold(
body: Padding(
padding: EdgeInsets.all(50.0),
child: Text('Loading'),
));
}
}
pls help me Im getting error while running the app:
Restarted application in 1,228ms.
I/flutter (24197): Error occured: NoSuchMethodError: The method 'substring' was called on null.
I/flutter (24197): Receiver: null
I/flutter (24197): Tried calling: substring(1, 3)
I/flutter (24197): {location: Florida, flag: img.jpg, time: Cannot Display Time Due to Error Occured}
I think I made DateTime Object thats why it is showing error, is there any alternative to this?
Any help will be much appreciated :)

Answer 1

The error you are getting is most likely because utc_offset is null.
You can check if it's actually null or not, and that it's length is at least 3 before performing substring(1,3) on it, like this:
String offset =
data['utc_offset'] == null || data['utc_offset'].length >= 3
? "utc offset has a problem"
: data['utc_offset'].substring(1, 3);