A list in form of a table can be sorted. One of the columns accepts empty values. If I sort the list by that column ascending, the empty values should be on top or at the bottom of the list? What if I sort it in descending order? Is it appropriate to put empty values always on top or always at the bottom of the list regardless of sorting order?
The most natural ordering strategy would be that items with an empty slot are ordered outside the items with filled slots, whether it'd be a descending or ascending list.
For example if you're sorting a list of products on the rate of the product in a descending order then you as a user is not the least interested in seeing the products that aren't rated at all first in the list, but rather last in the list. In that instance the absence of a value makes it non interesting.
Same if you're sorting a list of restaurants on the distance they are from you in an ascending order, then you as a user most probably want the ones with the lowest distance highest up in the list. Items that can't provide a distance from you are not relevant since that is the value you're after.
So to summarize, when ordering on a column in ascending or descending order as a rule you should order the items with an empty value last since they can't provide the user with the value they're after.