How to ignore empty fields in sort

I have a bootstrap table with a column (called: prio) where I can enter a number in a text input.

Like this:

This column should be sorted from low to high numbers, so first 1 then 2 then 3 etc. But if I sort that way, it first shows the empty cells, and at the bottom it shows 1,2,3 etc.

How can I make sure the empty cells are ignored in the sort?