我正在尝试运行命令“flutter packages pub run build_runner build”，但返回时出现错误，有人可以帮助我吗？ 这是我的代码这是回报

如何解决我正在尝试运行命令“flutter packages pub run build_runner build”，但返回时出现错误，有人可以帮助我吗？ 这是我的代码这是回报

我正在尝试运行命令“Flutter packages pub run build_runner build”，但返回时出现错误，有人可以帮助我吗？？

这是我的代码

---

import 'package:chopper/chopper.dart';

part 'post_api_service.chopper.dart';

@ChopperApi(baseUrl: 'https://jsonplaceholder.typicode.com/posts')
abstract class PostApiService extends ChopperService {
  @Get()
  Future<Response> getPosts();

  @Get(path: '/{id}')
  Future<Response> getPost(@Path('id') int id);

  @Post()
  Future<Response> postPost(
    @Body() Map<String,dynamic> body,);
}

---

这是回报

PS C:\srs\innovation\chopper\chopper_api> Flutter packages pub run build_runner build
[INFO] Generating build script...
[INFO] Generating build script completed,took 414ms

[WARNING] Invalidated precompiled build script due to missing asset graph.
[INFO] Precompiling build script......
[INFO] Precompiling build script... completed,took 1.1s

[SEVERE]
type 'Null' is not a subtype of type 'String' in type cast
pub finished with exit code 78
PS C:\srs\innovation\chopper\chopper_api>