Element UI version

2.12.0

OS/Browsers version

FF 60 / Chrome 76

Vue version

2.6.10

Reproduction Link

https://jsfiddle.net/14rey29c/

Steps to reproduce

Sort table column which contain null or undefined or empty values

What is Expected?

Rows with null or undefined or empty values should be at the end or the beginning of the table, depending on the sort direction

What is actually happening?

Rows with null or undefined or empty values aren't sorted and seem to be at randomly position