गेट्टर 'पोकेमॉन' को नल पर बुलाया गया था

मैं एक पोकेमॉन ऐप बनाने की कोशिश कर रहा हूं। लेकिन मुझे यह त्रुटि मिलती है:

"गेटर 'पोकेमॉन' को शून्य पर बुलाया गया था।

रिसीवर: शून्य

कॉल करने की कोशिश की: पोकेमॉन"

मैं डेटा के लिए इस एपीआई यूआरएल का उपयोग कर रहा हूँ "https://raw.githubusercontent.com/Biuni/PokemonGO-Pokedex/master/pokedex.json"

और मेरी पोकेमॉन क्लास यहाँ है:

class PokeHub {
  List<Pokemon> pokemon;

  PokeHub({this.pokemon});

  PokeHub.fromJson(Map<String,dynamic> json) {
    if (json['pokemon'] != null) {
      pokemon = new List<Pokemon>();
      json['pokemon'].forEach((items) {
        pokemon.add(new Pokemon.fromJson(items));
      });
    }
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    if (this.pokemon != null) {
      data['pokemon'] = this.pokemon.map((items) => items.toJson()).toList();
    }
    return data;
  }
}

class Pokemon {
  int id;
  String num;
  String name;
  String img;
  List<String> type;
  String height;
  String weight;
  String candy;
  int candyCount;
  String egg;
  String spawnChance;
  String avgSpawns;
  String spawnTime;
  List<double> multipliers;
  List<String> weaknesses;
  List<NextEvolution> nextEvolution;

  Pokemon(
      {this.id,
        this.num,
        this.name,
        this.img,
        this.type,
        this.height,
        this.weight,
        this.candy,
        this.candyCount,
        this.egg,
        this.spawnChance,
        this.avgSpawns,
        this.spawnTime,
        this.multipliers,
        this.weaknesses,
        this.nextEvolution});

  Pokemon.fromJson(Map<String, dynamic> json) {
    id = json['id'];
    num = json['num'];
    name = json['name'];
    img = json['img'];
    type = json['type'].cast<String>();
    height = json['height'];
    weight = json['weight'];
    candy = json['candy'];
    candyCount = json['candy_count'];
    egg = json['egg'];
    spawnChance = json['spawn_chance'].toString();
    avgSpawns = json['avg_spawns'].toString();
    spawnTime = json['spawn_time'];
    multipliers = json['multipliers']?.cast<double>();
    weaknesses = json['weaknesses'].cast<String>();
    if (json['next_evolution'] != null) {
      nextEvolution = new List<NextEvolution>();
      json['next_evolution'].forEach((v) {
        nextEvolution.add(new NextEvolution.fromJson(v));
      });
    }
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['id'] = this.id;
    data['num'] = this.num;
    data['name'] = this.name;
    data['img'] = this.img;
    data['type'] = this.type;
    data['height'] = this.height;
    data['weight'] = this.weight;
    data['candy'] = this.candy;
    data['candy_count'] = this.candyCount;
    data['egg'] = this.egg;
    data['spawn_chance'] = this.spawnChance;
    data['avg_spawns'] = this.avgSpawns;
    data['spawn_time'] = this.spawnTime;
    data['multipliers'] = this.multipliers;
    data['weaknesses'] = this.weaknesses;
    if (this.nextEvolution != null) {
      data['next_evolution'] =
          this.nextEvolution.map((v) => v.toJson()).toList();
    }
    return data;
  }
}

class NextEvolution {
  String num;
  String name;

  NextEvolution({this.num, this.name});

  NextEvolution.fromJson(Map<String, dynamic> json) {
    num = json['num'];
    name = json['name'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['num'] = this.num;
    data['name'] = this.name;
    return data;
  }

और यह मेरी main.dart फ़ाइल है:

import 'package:flutter/material.dart';
import 'package:pokemon_flutter/screens/main_screen.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: "Poke App",
      home: MainScreen(),
      debugShowCheckedModeBanner: false,
    );
  }

}

और यह मेरी main_screen.dart फ़ाइल है:

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';

import 'package:pokemon_flutter/models/pokemon.dart';

class MainScreen extends StatefulWidget {
  @override
  _MainScreenState createState() => _MainScreenState();
}

class _MainScreenState extends State<MainScreen> {
  var url =
      "https://raw.githubusercontent.com/Biuni/PokemonGO-Pokedex/master/pokedex.json";
  PokeHub pokeHub;
  @override
  void initState() {
    super.initState();
    fetchData();
  }

  void fetchData() async {
    var res = await http.get(url);
    var decodedJson = jsonDecode(res.body);
    pokeHub = PokeHub.fromJson(decodedJson);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Poke App"),
        backgroundColor: Colors.cyan,
      ),
      body: GridView.count(
        crossAxisCount: 2,
        children: pokeHub.pokemon.map((poke) => Card()).toList(),
      ),
      drawer: Drawer(),
      floatingActionButton: FloatingActionButton(
        onPressed: () {},
        backgroundColor: Colors.cyan,
        child: Icon(Icons.refresh),
      ),
    );
  }
}

ऐसा लगता है कि सब कुछ सच है इसलिए मैं गलती को नहीं पहचान सकता। यदि आपके पास इस स्थिति के लिए कोई सलाह है तो मेरी सराहना की जाएगी।

संपादित करें: मैं यहां नया हूं इसलिए कभी-कभी मेरे प्रश्न व्यर्थ हो सकते हैं। लेकिन कृपया मेरे अंक कम न करें। स्टैक ओवरफ्लो अब मेरे प्रश्नों को स्वीकार नहीं करेगा। कृपया मेरे अंक बढ़ाएँ।