Results 4 comments of lp's man

`sss` ![image](https://user-images.githubusercontent.com/22695827/60933255-1801c580-a2f4-11e9-9e72-5dfff0381458.png)

Can anybody explain that?

看了源码,发现empty不是用在数据为空的时候的, @jikkai @Leopoldthecoder @QingWei-Li 向大佬们提个需求