Flutter ERROR : TypeErrorImpl was thrown while handling a gesture

Question

Hello i was trying to get images from my pc to firebase storage . then saving the url and showing them through the firestore. code for defining

final FirebaseStorage _storage = FirebaseStorage.instance;
  final FirebaseFirestore _firestore = FirebaseFirestore.instance;
  dynamic _imageFile;
  String? _fileName = '';
  pickImage() async {
    FilePickerResult? result = await FilePicker.platform.pickFiles(
      allowMultiple: false,
      type: FileType.custom,
      allowedExtensions: ['jpg', 'png', 'jpeg'],
    );
    if (result != null) {
      setState(() {
        _imageFile = result.files.first.bytes;
        _fileName = result.files.first.name;
      });
    }
  }

  _uploadbannerToStorage(dynamic image) async {
    Reference ref = _storage.ref().child('Banners').child(_fileName!);
    UploadTask uploadTask = ref.putData(image);
    TaskSnapshot snapshot = await uploadTask;
    String downloadURL = await snapshot.ref.getDownloadURL();
    return downloadURL;
  }

  _uploadBannerToFirestore(String downloadURL) async {
    if (_imageFile != null) {
      String image = await _uploadbannerToStorage(_imageFile);
      await _firestore.collection('Banners').doc(_fileName).set({
        'image': image,
      });
    }
  }

dependencies:

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:file_picker/file_picker.dart';
import 'package:firebase_storage/firebase_storage.dart';

but I get this error everytime I try to save Image

The following TypeErrorImpl was thrown while handling a gesture: Expected a value of type 'String', but got one of type 'NativeUint8List'

I tried casting downloadURL but that doest help I also thought about using Image_picker but there is little to no support for web in it and my program is to be used primarily on web.