Android音乐，播放列表填充报错 ?报错

setListAdpter往ListView添加内容报错
activity方法

 public void setListAdpter(List<HashMap<String, String>> mp3list) {  
        mAdapter = new SimpleAdapter(this, mp3list,R.layout.activity_music__list, 
                new String[] { "title", "Artist", "duration" }, 
                new int[] { R.id.music_title,  R.id.music_Artist, R.id.music_duration });  
        musicLists.setAdapter(mAdapter);  
    }

报错内容：
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.zjh.music/com.zjh.music.Activity.Music_List_Activity}: java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference