Retrofit2.0 得到 MalformedJsonException 而 json 似乎正确

我的Android应用程序使用的是RETERFIT:2.0.0-Beta4.

我试图添加一个改型用户，该用户已在数据库中正确创建，但出现以下错误:

03-14 06:04:27.731 30572-30600/com.lehuo.lehuoandroid D/OkHttp: CALLING POST SP_User_CreateUser....your new user_id:48
{"data":{"user_id":"48","nickname":null,"password":null,"status":null},"status":1,"msg":"OK"}
03-14 06:04:27.731 30572-30600/com.lehuo.lehuoandroid D/OkHttp: <-- END HTTP (147-byte body)
03-14 06:04:27.732 30572-30600/com.lehuo.lehuoandroid E/My Jobs: error while executing job
     com.google.gson.stream.MalformedJsonException: Use JsonReader.setLenient(true) to accept malformed JSON at line 1 column 1 path $
         at com.google.gson.stream.JsonReader.syntaxError(JsonReader.java:1573)
         at com.google.gson.stream.JsonReader.checkLenient(JsonReader.java:1423)
         at com.google.gson.stream.JsonReader.doPeek(JsonReader.java:587)
         at com.google.gson.stream.JsonReader.peek(JsonReader.java:429)
         at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:202)
         at com.google.gson.TypeAdapter.fromJson(TypeAdapter.java:260)
         at retrofit2.converter.gson.GsonResponseBodyConverter.convert(GsonResponseBodyConverter.java:32)
         at retrofit2.converter.gson.GsonResponseBodyConverter.convert(GsonResponseBodyConverter.java:23)
         at retrofit2.OkHttpCall.parseResponse(OkHttpCall.java:213)
         at retrofit2.OkHttpCall.execute(OkHttpCall.java:177)
         at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall.execute(ExecutorCallAdapterFactory.java:87)
         at com.lehuo.lehuoandroid.async.NetworkJob.callNet(NetworkJob.java:30)
         at com.lehuo.lehuoandroid.async.CreateUserJob.onRun(CreateUserJob.java:34)
         at com.path.android.jobqueue.BaseJob.safeRun(BaseJob.java:108)
         at com.path.android.jobqueue.JobHolder.safeRun(JobHolder.java:60)
         at com.path.android.jobqueue.executor.JobConsumerExecutor$JobConsumer.run(JobConsumerExecutor.java:201)
         at java.lang.Thread.run(Thread.java:818)

The returned result from server is :

{"data":{"user_id":"48","nickname":null,"password":null,"status":null},"status":1,"msg":"OK"}

This is correct json format, I don't understand why I get such exception?

Here us my interface:

public class ApiResult<T> {
    public T data;
    public int status;
    public String msg;
}

public interface ApiUsers {
    @POST("/users/new")
    public Call<ApiResult<User>> createUser(@Body User user);
}

public class User {
    public int user_id;
    public String registration;
    public int registration_type;
    public String avatar;
    public String nickname;
    public String password;
    public String status;

}

public class Api {

    // TODO modify the value
    public static final String BASE_URL = "xxx";

    private static Api instance = new Api();

    public static Api getInstance() {
        return instance;
    }

    private Api(){}

    public Retrofit getRetrofit() {
        HttpLoggingInterceptor interceptor = new HttpLoggingInterceptor();
        interceptor.setLevel(HttpLoggingInterceptor.Level.BODY);
        OkHttpClient client = new OkHttpClient.Builder()
                .addInterceptor(interceptor)
                .retryOnConnectionFailure(true)
                .connectTimeout(15, TimeUnit.SECONDS)
                .build();

        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl(BASE_URL)
                .client(client)
                .addConverterFactory(GsonConverterFactory.create())
                .build();

        return retrofit;
    }

    public <S> S createService(Class<S> serviceClass) {
        return getRetrofit().create(serviceClass);
    }
}

The caller code is:

ApiUsers api = Api.getInstance().createService(ApiUsers.class);
Call<ApiResult<User>> call = api.createUser(user);
CreateUserMessage message = new CreateUserMessage();
callNet(call, message);

Could anyone give any clue?