在Google App Engine上返回空列表的行为在开发服务器上和部署时有所不同

我创建了一个返回项目列表的端点。当列表为空时，我期待在JSON中看到一个空列表，但列表字段被省略。这不是在开发服务器上发生的事情。

I've created an endpoint that returns a list of items. When the list is empty, I was expecting to see an empty list in the JSON, but the list field was instead omitted. That's not what happens on the dev server.

例：

Ex:

@ApiMethod(name = "udinic", path = "udinic")
public List<UdinicResponse> getUdinics() {
    List<UdinicResponse> list = new ArrayList<>();

    UdinicResponse res = new UdinicResponse();
    res.bla = "sds";
    list.add(res);

    return list;
}

static class UdinicResponse {
    String bla;

    public String getBla() {
        return bla;
    }

    public void setBla(String bla) {
        this.bla = bla;
    }
}

当我在dev服务器上运行这个时，我得到的答复：

When I run this on the dev server, that's the response I get:

{
items: [ ]
}

当它位于部署的服务器上时，这就是我得到的结果：

When it's on the deployed server, that's what I get:

{
kind: "udinicEndpoint#resourcesItem",
etag: ""3Ms41gaYW9qnDr8JAXr8FIDhu9jVetg""
}

任何想法如何获得一致的行为？我希望获得一个空列表，而不是省略该字段。

Any ideas how can I get a consistent behavior? I prefer to get an empty list instead of omitting the field.