新手提问，刚学，还不太懂，下面第一句语句很基本的语句，执行之后sql为空。请大牛指点是怎么回事，谢谢！
Sql sql = Sqls.queryRecord("SELECT DATE(register_time),channel_number,COUNT(user_id),SUM(fraction) FROM app_user GROUP BY DATE(register_time)");
Pager pager = new OffsetPager(start, length);
sql.setPager(pager);
dao.execute(sql);
我搜了以前的帖子，有提到是不是忘了设置refer，请问是什么问题？如果是忘了refer，该怎么设置？谢谢！
以前的提问帖子：https://nutz.cn/yvr/t/40ga15pcdajinrqr4e9cjheant

报错信息：
[ERROR] 2018-11-09 03:00:17,780 cn.wizzer.modules.controllers.platform.channelBa
ckend.ChannelBackendControllers.data(ChannelBackendControllers.java:107) - null
[DEBUG] 2018-11-09 03:00:17,781 cn.wizzer.common.processor.LogTimeProcessor.proc
ess(LogTimeProcessor.java:26) - [POST]URI=/admin/platform/channelBackend/data 84
ms
[WARN ] 2018-11-09 03:00:17,784 org.nutz.mvc.impl.processor.FailProcessor.proces
s(FailProcessor.java:28) - Error@/platform/channelBackend/data :
java.lang.NullPointerException
at cn.wizzer.modules.controllers.platform.channelBackend.ChannelBackendC
ontrollers.data(ChannelBackendControllers.java:111)