RxAndroid 2.x subscribe 疑问

以下为我的代码

@POST("/hospital/department/list")
    Observable<ResponseBody> list(@Body Department department);

public Observable<String> list(Department department) {
        return departmentAPI.list(department)
                .flatMap((Function<ResponseBody, ObservableSource<String>>) responseBody -> Observable.just(responseBody.string()));
    }

 private void initDepOptions() {
        final ProgressDialog progressDialog = new ProgressDialog(getContext());
        depDataManager.list(tDepartment)
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .doOnSubscribe(disposable -> {
                    progressDialog.setMessage(LOADING_MESSAGE);
                    progressDialog.show();
                })
                .doOnComplete(() -> progressDialog.dismiss())
                .subscribe(new RxSubscriber<String>() {
                    @Override
                    public void onNext(String s) {
                        ApiResponse response = GsonParser.fromJSONObject(s, ApiResponse.class);
                        if (response.success()) {
                            transform2DepartmentList(response.data);
                        } else {
                            Toasty.error(getContext(), response.message, Toast.LENGTH_LONG, true).show();
                        }
                    }
                });
    }

我准备用其来获取服务端 json 数据并反序列化，可是这时候出现了一个问题，subscribe 中的 onNext 方法并未执行...

ps:
RxSubscriber

public class RxSubscriber<T> extends DisposableObserver<T> {
    
    @Override
    public void onNext(@NonNull T t) {
        
    }
    
    @Override
    public void onError(@NonNull Throwable e) {
        
    }
    
    @Override
    public void onComplete() {
        
    }
}