Retrofit 2.2.0从响应中获取特定字段，而不是绑定到对象

Question

在Android客户端上我正在使用HTTP请求的改造，我遇到了GET方法的问题;我如何获取用户的特定字段，例如，我想将用户名存储到变量name = response.getUserName();中。界面因某种原因始终返回null

 //This the API GET
@GET("api/user")
Call<List<Users>> listUsers();

//This is the restClient
/**
 * Getting all the users from the
 * REST API and mongoDB
 * @return
 */
public List<Users> getUsers(){
    Call<List<Users>> userList = service.listUsers();
    userList.enqueue(new Callback<List<Users>>() {
        @Override
        public void onResponse(Call<List<Users>> call, Response<List<Users>> response) {

            /**
             * The is isSuccessful method find out
             * if the status code is in the range 200-300,
             * indicating success.
             */
            if(response.isSuccessful()){
                users = response.body();                     
                callback.resultReady(users);
            }
        }

//Here is the callbackInterface
public interface ResulReadyCallBack {
public void resultReady(List<Users> users);

}