源码

public class MusicData {
    private SongMusic mSongMusic;
    private Retrofit mRetrofit;
    private static MusicData mData=new MusicData();
    private MusicData(){}
    public HttpApi getHttp(){
        if(mRetrofit==null){
            mRetrofit=new Retrofit.Builder().baseUrl("http://tingapi.ting.baidu.com/")
                    .addConverterFactory(GsonConverterFactory.create())
                    .build();
        }
        return mRetrofit.create(HttpApi.class);
    }
    
    public void getListMusic(int type, int size, int off){
        Call<RecommentBean> mCall=getHttp().getrecomment(type,size,off);
        mCall.enqueue(new Callback<RecommentBean>() {
            @Override
            public void onResponse(Call<RecommentBean> call, Response<RecommentBean> response) {
                mSongMusic.setAdapter(response.body().getSong_list());
            }

            @Override
            public void onFailure(Call<RecommentBean> call, Throwable t) {

            }
        });
    }
//设置接口实现类的对象
    public void setSongServer(SongMusic song){
        mSongMusic=song;
    }
    public static MusicData getMusicData(){
        return mData;
    }
}

错误
E/AndroidRuntime: FATAL EXCEPTION: main

              Process: com.wang.mymusic, PID: 3414
              java.lang.NullPointerException: Attempt to invoke virtual method 'java.util.List com.wang.mymusic.model.RecommentBean.getSong_list()' on a null object reference
                  at com.wang.mymusic.data.MusicData$2.onResponse(MusicData.java:50)
                  at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall$1$1.run(ExecutorCallAdapterFactory.java:68)
                  at android.os.Handler.handleCallback(Handler.java:739)
                  at android.os.Handler.dispatchMessage(Handler.java:95)
                  at android.os.Looper.loop(Looper.java:148)
                  at android.app.ActivityThread.main(ActivityThread.java:5417)
                  at java.lang.reflect.Method.invoke(Native Method)
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

描述
这块是使用retrofit2请求音乐列表，并将请求放在一个工具类中的方法里，使用接口将返回值传递给需要使用返回数据的页面，但是在编译运行时报错；但是该请求代码放在activity中的时候是正确的，可以正常获得数据，在网上着也没有搜索到解决方法，不知道是哪里出错了