Class '_InternalLinkedHashMap<String, dynamic>' has no instance getter 'code' flutter

im trying to call an api. This is my model;

// To parse this JSON data, do
//
//     final hisselist = hisselistFromJson(jsonString);

import 'dart:convert';

Hisselist hisselistFromJson(String str) => Hisselist.fromJson(json.decode(str));

String hisselistToJson(Hisselist data) => json.encode(data.toJson());

class Hisselist {
  Hisselist({
    required this.success,
    required this.result,
  });

  bool success;
  List<dynamic> result;

  factory Hisselist.fromJson(Map<String, dynamic> json) => Hisselist(
    success: json["success"],
    result: List<dynamic>.from(json["result"].map((x) => x)),
  );

  Map<String, dynamic> toJson() => {
    "success": success,
    "result": List<dynamic>.from(result.map((x) => x)),
  };
}

class ResultClass {
  ResultClass({
    required this.rate,
    required this.lastprice,
    required this.lastpricestr,
    required this.hacim,
    required this.hacimstr,
    required this.text,
    required this.code,
  });

  double rate;
  double lastprice;
  String lastpricestr;
  double hacim;
  String hacimstr;
  String text;
  String code;

  factory ResultClass.fromJson(Map<String, dynamic> json) => ResultClass(
    rate: json["rate"].toDouble(),
    lastprice: json["lastprice"].toDouble(),
    lastpricestr: json["lastpricestr"],
    hacim: json["hacim"].toDouble(),
    hacimstr: json["hacimstr"],
    text: json["text"],
    code: json["code"],
  );

  Map<String, dynamic> toJson() => {
    "rate": rate,
    "lastprice": lastprice,
    "lastpricestr": lastpricestr,
    "hacim": hacim,
    "hacimstr": hacimstr,
    "text": text,
    "code": code,
  };
}

And my page which I call api is :

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

import '../models/apis/hisselist.dart';

class Stocks extends StatefulWidget {
  Stocks({Key? key}) : super(key: key);

  @override
  _StocksState createState() => _StocksState();
}

class _StocksState extends State<Stocks> with AutomaticKeepAliveClientMixin {



  ScrollController? controller;
  final scaffoldKey = GlobalKey<ScaffoldState>();
  final url = Uri.parse('https://api.collectapi.com/economy/hisseSenedi');
  var counter;
  Hisselist? hisseResult;

  Future callHisse() async {
    try{
      Map<String, String> requestHeaders = {
        'Content-Type': 'application/json',
        'Authorization': 'xxx'
      };
      final response = await http.get(url,headers:requestHeaders);

      if(response.statusCode == 200){
        var result = hisselistFromJson(response.body);

        if(mounted);
        setState(() {
          counter = result.result.length;
          hisseResult = result;
        });
        return result;
      } else {
        print(response.statusCode);
      }
    } catch(e) {
      print(e.toString());
    }
  }
  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    callHisse();
  }
  @override
  Widget build(BuildContext context) {
    super.build(context);

    return Scaffold(
      appBar: AppBar(
        centerTitle: false,
        automaticallyImplyLeading: false,
        title: Text(
            'Hisseler'
        ),
      ),
      body: Center(
        child: Padding(
          padding: const EdgeInsets.all(8.0),
          child: counter != null ?

          ListView.builder(
              itemCount: counter,
              itemBuilder: (context, index){
                return Card(
                  child: ListTile(
                    title: Text(hisseResult?.result[index].code??""),
                    subtitle: Text(hisseResult?.result[index].code??""),                  ),
                );
          }) : Center(child: CircularProgressIndicator(

          )),
        ),
      ),

    );


  }

  @override
  bool get wantKeepAlive => true;
}

I get this error; Class '_InternalLinkedHashMap<String, dynamic>' has no instance getter 'code'. Receiver: _LinkedHashMap len:12 Tried calling: code

How can I fix this? Thanks for your help

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

Hisselist hisselistFromJson(String str) => Hisselist.fromJson(json.decode(str));

String hisselistToJson(Hisselist data) => json.encode(data.toJson());

class Hisselist {
  Hisselist({
    this.success,
    this.result,
  });

  bool? success;
  List<Result>? result;

  factory Hisselist.fromJson(Map<String, dynamic> json) => Hisselist(
        success: json["success"],
        result: List<Result>.from(json["result"].map((x) => Result.fromJson(x))),
      );

  Map<String, dynamic> toJson() => {
        "success": success,
        "result": List<dynamic>.from(result!.map((x) => x.toJson())),
      };
}

class Result {
  Result({
    this.rate,
    this.lastprice,
    this.lastpricestr,
    this.hacim,
    this.hacimstr,
    this.text,
    this.code,
  });

  double? rate;
  double? lastprice;
  String? lastpricestr;
  double? hacim;
  String? hacimstr;
  String? text;
  String? code;

  factory Result.fromJson(Map<String, dynamic> json) => Result(
        rate: json["rate"].toDouble(),
        lastprice: json["lastprice"].toDouble(),
        lastpricestr: json["lastpricestr"],
        hacim: json["hacim"].toDouble(),
        hacimstr: json["hacimstr"],
        text: json["text"],
        code: json["code"],
      );

  Map<String, dynamic> toJson() => {
        "rate": rate,
        "lastprice": lastprice,
        "lastpricestr": lastpricestr,
        "hacim": hacim,
        "hacimstr": hacimstr,
        "text": text,
        "code": code,
      };
}

class Stocks extends StatefulWidget {
  Stocks({Key? key}) : super(key: key);

  @override
  _StocksState createState() => _StocksState();
}

class _StocksState extends State<Stocks> with AutomaticKeepAliveClientMixin {
  ScrollController? controller;
  final scaffoldKey = GlobalKey<ScaffoldState>();
  final url = Uri.parse('https://api.collectapi.com/economy/hisseSenedi');
  var counter;
  Hisselist? hisseResult;

  Future callHisse() async {
    try {
      Map<String, String> requestHeaders = {'Content-Type': 'application/json', 'Authorization': 'xxx'};
      final response = await http.get(url, headers: requestHeaders);

      if (response.statusCode == 200) {
        Hisselist result = hisselistFromJson(response.body);

        if (mounted) ;
        setState(() {
          counter = result.result!.length;
          hisseResult = result;
        });
        return result;
      } else {
        print(response.statusCode);
      }
    } catch (e) {
      print(e.toString());
    }
  }

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    callHisse();
  }

  @override
  Widget build(BuildContext context) {
    super.build(context);

    return Scaffold(
      appBar: AppBar(
        centerTitle: false,
        automaticallyImplyLeading: false,
        title: Text('Hisseler'),
      ),
      body: Center(
        child: Padding(
          padding: const EdgeInsets.all(8.0),
          child: counter != null
              ? ListView.builder(
                  itemCount: counter,
                  itemBuilder: (context, index) {
                    return Card(
                      child: ListTile(
                        title: Text(hisseResult?.result![index].code ?? ""),
                        subtitle: Text(hisseResult?.result![index].code ?? ""),
                      ),
                    );
                  })
              : Center(child: CircularProgressIndicator()),
        ),
      ),
    );
  }

  @override
  bool get wantKeepAlive => true;
}