如何使用flutter处理url中的空图像错误

import 'package:flutter/material.dart';
import 'package:dio/dio.dart';
import 'package:cached_network_image/cached_network_image.dart';

class ImageScreen extends StatefulWidget {
  final String imageUrl;

  ImageScreen({required this.imageUrl});

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

class _ImageScreenState extends State<ImageScreen> {
  late Future<Response> _imageFuture;

  @override
  void initState() {
    super.initState();
    _imageFuture = _fetchImage();
  }

  Future<Response> _fetchImage() async {
    final dio = Dio();
    return dio.get(widget.imageUrl);
  }

  @override
  Widget build(BuildContext context) {
    return FutureBuilder<Response>(
      future: _imageFuture,
      builder: (context, snapshot) {
        if (snapshot.connectionState == ConnectionState.done) {
          if (snapshot.hasError) {
            // 图像加载失败时显示错误提示
            return Text('Failed to load image');
          }
          if (snapshot.data?.statusCode == 200) {
            // 图像加载成功时显示图像
            return CachedNetworkImage(
              imageUrl: widget.imageUrl,
              placeholder: (context, url) => CircularProgressIndicator(),
              errorWidget: (context, url, error) => Icon(Icons.error),
            );
          }
        }
        // 加载过程中显示加载指示器
        return CircularProgressIndicator();
      },
    );
  }
}

void main() {
  runApp(MaterialApp(
    home: ImageScreen(imageUrl: 'https://example.com/image.jpg'),
  ));
}