我不明白为什么在flutter中使用image_picker时会出现这个错误

import 'package:flutter/material.dart';
import 'package:image_picker/image_picker.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: ImagePickerExample(),
    );
  }
}

class ImagePickerExample extends StatefulWidget {
  @override
  _ImagePickerExampleState createState() => _ImagePickerExampleState();
}

class _ImagePickerExampleState extends State<ImagePickerExample> {
  final ImagePicker _picker = ImagePicker();
  XFile? _image;

  Future<void> _pickImage() async {
    final pickedFile = await _picker.pickImage(source: ImageSource.camera);
    setState(() {
      _image = pickedFile;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Image Picker Example')),
      body: Center(
        child: _image == null
            ? Text('No image selected.')
            : Image.file(File(_image!.path)),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _pickImage,
        tooltip: 'Pick Image',
        child: Icon(Icons.add_a_photo),
      ),
    );
  }
}