改装+GSON不会序列化HashMap,GSON自己会

我的请求模型包含地图,看起来像

public class AddRequest {
public String url;
public String key;
public Map<String, String> attributes;

public AddProductToBasketRequest(String url, String key, Map<String, String> attributes) {
    this.url = url;
    this.key = key;
    this.attributes = attributes;
}

}

当我打印我的模型时

new Gson().toJson(request)

我有

{"url":"https://www.net-a-porter.com/lalala","attributes":{"size":"it34"},"key":"agtzfnNm"}

但当我通过改造发送请求时,日志中有空属性

{"attributes": {}, "url": "https://www.net-a-porter.com/lalala", "key": "agtzfnNm"}   

我的RestAdapter看起来像

public RestAdapter restAdapter = new RestAdapter.Builder()
        .setRequestInterceptor(new RequestInterceptor() {
            @Override
            public void intercept(RequestFacade request) {
                request.addHeader("Access-Token", token;
            }
        })
        .setEndpoint(url)
        .setConverter(new GsonConverter(new GsonBuilder()
                .excludeFieldsWithModifiers(Modifier.FINAL, Modifier.TRANSIENT, Modifier.STATIC)
                .serializeNulls()
                .create()))
        .build();

执行请求的代码如下

AddInterface restInterface = restAdapter.create(AddInterface.class);
restInterface.request(id, request, new Callback<Basket>() {
    @Override
    public void success(Basket basket, Response r) {
    }

    @Override
    public void failure(RetrofitError error) {
    }
});