title: Error by reading simple Json File - The getter 'visible' was called on null
body: <p>First of all, I am new to flutter, dart and also StackOverflow.. </p>
  
  <p>I just wanted to experience some first insights to flutter and parsing a json file.
  However I am getting an error, that the getter 'visible' was called on null.</p>
  
  <p>By going to the debug mode in flutter, I can clearly see all the data provided from the API, but the frontend just shows nothing.
  Just the mentioned error in the debug console.</p>
  
  <p>This is the very simple code:</p>
  
  <pre><code>import 'dart:convert';
  
  import 'package:flutter/material.dart';
  import 'package:http/http.dart' as http;
  
  void main() =&gt; runApp(MyApp());
  
  class MyApp extends StatelessWidget {
    @override
    Widget build(BuildContext context) {
      return MaterialApp(
        title: 'JSON',
        home: Scaffold(
          appBar: AppBar(
            title: Text('JSON'),
          ),
          body: Container(
            child: FutureBuilder&lt;List&lt;User&gt;&gt;(
                future: fetchListUser(),
                builder: (context, snapshot) {
                  if (snapshot.connectionState == ConnectionState.done) {
                    List&lt;User&gt; users = snapshot.data;
                    return ListView(
                      children: users.map((user) {
                        Text('UserName: ${user.username}');
                      }).toList(),
                    );
                  } else {
                    return CircularProgressIndicator();
                  }
                }),
          ),
        ),
      );
    }
  }
  
  Future&lt;List&lt;User&gt;&gt; fetchListUser() async {
    final response = await http.get('https://jsonplaceholder.typicode.com/users');
    if (response.statusCode == 200) {
      List users = json.decode(response.body);
      return users.map((user) =&gt; User.fromJson(user)).toList();
    } else
      throw Exception('Failed to Load Users');
  }
  
  class User {
    final int id;
    final String name, username, email, phone, website;
    final Adresse adress;
    final Company company;
  
    User({
      this.id,
      this.name,
      this.adress,
      this.company,
      this.email,
      this.phone,
      this.username,
      this.website,
    });
  
    factory User.fromJson(Map&lt;String, dynamic&gt; json) {
      return User(
        adress: Adresse.fromJson(json['address']),
        company: Company.fromJson(json['company']),
        email: json['email'],
        id: json['id'],
        name: json['name'],
        phone: json['phone'],
        username: json['username'],
        website: json['website'],
      );
    }
  }
  
  class Adresse {
    final String street, suite, zipcide;
    final Geo geo;
  
    Adresse({this.geo, this.street, this.suite, this.zipcide});
  
    factory Adresse.fromJson(Map&lt;String, dynamic&gt; json) {
      return Adresse(
        geo: Geo.fromJson(json['geo']),
        street: json['street'],
        suite: json['suite'],
        zipcide: json['zipcode'],
      );
    }
  }
  
  class Geo {
    final String lat, lng;
  
    Geo({this.lat, this.lng});
  
    factory Geo.fromJson(Map&lt;String, dynamic&gt; json) {
      return Geo(
        lat: json['lat'],
        lng: json['lng'],
      );
    }
  }
  
  class Company {
    final String name;
    final String catchPhrase;
    final String bs;
  
    Company({this.bs, this.catchPhrase, this.name});
  
    factory Company.fromJson(Map&lt;String, dynamic&gt; json) {
      return Company(
        bs: json['bs'],
        catchPhrase: json['catchPhrase'],
        name: json['name'],
      );
    }
  }
  </code></pre>
  
  <p>Its really just building some classes for the json structure and then I just wanted to output something.</p>
  
  <p>Can anybody help me? :)</p>
  
  <p>Thanks!</p>