安卓AVUser查询子类错误，求解决
查询一组User的子类，但是请求下来的list没办法转换成子类

代码如下
YSUser currentYSUser = (YSUser) YSUser.getCurrentUser();
Log.d("用户", currentYSUser.getName()+currentYSUser.getCity()+"");
AVRelation relation = currentYSUser.getRelation("contacts");

			AVQuery<YSUser> query1 = relation.getQuery();
			query1.findInBackground(new FindCallback<YSUser>() {

				@Override
				public void done(List<YSUser> buddyList, AVException error) {
					// TODO Auto-generated method stub
					if(error==null)
					{
						YSUser user=buddyList.get(0);
						Log.d("user", user.getName());
					}
					else
					{

					}
				}
			});

结果会报错
：java.lang.ClassCastException: com.avos.avoscloud.AVUser cannot be cast to com.zstech.leancloudclass.YSUser

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