Flutter The method 'map' was called on null. Receiver: null error – Phpmyadmin

I’m having this super annoying issue of being unable to grab and display a table from my server hosted on PhpmyAdmin. (I’ve managed to grab the data and have it printed in the console, but now that I’m trying to display it in a table I can’t seem to get it working)

I’ve tried nulling my variables but I’m not really sure what the main culprit for this error is. Any help would be greatly appreciated.

Image of Error

data.dart File

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

  @override
  State<dataListing> createState() => _dataListingState();
}

class _dataListingState extends State<dataListing> {
  @override
  Widget build(BuildContext context) {
    return Container();
  }
}

class listingData{
  String? ListingID, listingName, listingDescription, address, suburbName, phoneNumber, openingHours, Email, Website;

  listingData({
    this.ListingID,
    this.listingName,
    this.listingDescription,
    this.address,
    this.suburbName,
    this.phoneNumber,
    this.openingHours,
    this.Email,
    this.Website,
  });
  //constructor
  List<listingData> datalist = [];
  factory listingData.fromJSON(Map<String, dynamic> json){
    return listingData(
      ListingID: json["ListingID"],
      listingName: json["listingName"],
      listingDescription: json["listingDescription"],
      address: json["address"],
      suburbName: json["suburbName"],
      phoneNumber: json["phoneNumber"],
      openingHours: json["openingHours"],
      Email: json["Email"],
      Website: json["Website"],
    );
  }
}

Directory.dart file

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'package:app/pages/data.dart';


class directoryPage extends StatefulWidget {
  @override
  State<directoryPage> createState() => _directoryPageState();
}

class _directoryPageState extends State<directoryPage> {

  // List serviceListing = [];
  //
  // getAllListing()async{
  //   String url = "URL HERE";
  //   var response = await http.get(Uri.parse(url));
  //   if (response.statusCode == 200){
  //     setState (() {
  //       serviceListing = json.decode(response.body);
  //     });
  //     print (serviceListing);
  //     return serviceListing;
  //   }
  // }
  bool error = false, dataloaded = false;
  var data;
  String dataurl = "URL HERE";


  @override
  void initState (){
    loaddata();
    super.initState();
    // getAllListing();
  }

  void loaddata() {
    Future.delayed(Duration.zero,() async {
      var res = await http.post(Uri.parse(dataurl));
      if (res.statusCode == 200) {
        setState(() {
          data = json.decode(res.body);
          dataloaded = true;

        });
      }
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text('Directory'),
          centerTitle: true,
          elevation: 0,
          backgroundColor: Color(0xFFA30B32),
          //WSU Appbar Icon
          leading: Padding(
            padding: const EdgeInsets.all(8.0),
            child: Image.asset("assets/wsulogo.png", scale: 8.0),
          ),
        ),
        body: Container(
          padding: EdgeInsets.all(15),
          child:dataloaded?datalist():
          Center(
            child:CircularProgressIndicator()
          ),
        )
    );
  }

  Widget datalist(){
    if(data["error"]) {
      return Text(data["errmsg"]);
    }else{
      List<listingData> datalist = List<listingData>.from(data["data"].map((i){
        return listingData.fromJSON(i);
      })
      );

      return Table( //if data is loaded then show table
        border: TableBorder.all(width:1, color:Colors.black45),
        children: datalist.map((listingdata){
          return TableRow( //return table row in every loop
              children: [
                //table cells inside table row
                TableCell(child: Padding(
                    padding: EdgeInsets.all(5),
                    child:Text(listingdata.ListingID!)
                )
                ),
                TableCell(child: Padding(
                    padding: EdgeInsets.all(5),
                    child:Text(listingdata.listingName!)
                )
                ),
                TableCell(child: Padding(
                    padding: EdgeInsets.all(5),
                    child:Text(listingdata.listingDescription!)
                )
                ),
                TableCell(child: Padding(
                    padding: EdgeInsets.all(5),
                    child:Text(listingdata.address!)
                )
                ),
              ]
          );
        }).toList(),
      );
    }
  }
}