I have a map screen where when I click on the button to draw a polygon nothing happens on the map. Is there any issue in my code files?

This is my `MapScreen`

import 'package:flutter/material.dart';
import 'package:flutter/services.dart' show rootBundle;
import 'package:mapbox_maps_flutter/mapbox_maps_flutter.dart';

class MapScreen extends StatefulWidget {
  const MapScreen({super.key});

  @override
  State createState() => MapScreenState();
}

class MapScreenState extends State<MapScreen> {
  MapboxMap? mapboxMap;
  var isLight = true;

  _onMapCreated(MapboxMap mapboxMap) async {
    this.mapboxMap = mapboxMap;
  }

  void drawPolygon() async {
    var data = await rootBundle.loadString('assets/mydata.geojson');
    await mapboxMap!.style.addSource(GeoJsonSource(
      id: "mydata",
      data: data,
    ));
    await mapboxMap!.style.addLayer(FillLayer(
        id: "mydata2",
        sourceId: "mydata",
        fillColor: Colors.red.value,
        fillOutlineColor: Colors.deepPurple.value));
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: Column(
      children: [
        SizedBox(
          height: 500,
          child: MapWidget(
            key: const ValueKey("mapWidget"),
            styleUri: MapboxStyles.DARK,
            cameraOptions: CameraOptions(
                center: Point(coordinates: Position(78.042, 30.3165)),
                zoom: 14.0),
            onMapCreated: _onMapCreated,
          ),
        ),
        ElevatedButton(
          onPressed: drawPolygon,
          child: const Text("Draw Polygon"),
        ),
      ],
    ));
  }
}

and this is my mydata.geojson file

{
  "data": {
    "type": "FeatureCollection",
    "features": [
      {
        "type": "Feature",
        "properties": {},
        "geometry": {
          "type": "Polygon",
          "coordinates": [
            [
              [78.042, 30.3165],
              [78.042, 30.3163],
              [78.043, 30.3166],
              [78.044, 30.3164],
              [78.042, 30.3165],
              [78.043, 30.3166],
              [78.044, 30.3164],
              [78.042, 30.3163],
              [78.042, 30.3165]
            ]
          ]
        }
      }
    ]
  }
}

But when I click on the button to draw the polygon nothing happens on the map and I’m not getting any error on the console side neither.