Data Validation List with only non-blank cells

I have a list in one worksheet which comes from "=SALESMEN!$D:$D" but the list is extremely long with blank values. How can I make the list only show values from column D which are non-blank? Thanks in advance.

Edit: Currently the list goes up to 30, however I want to use all of Column D from the SALESMEN worksheet, that way if I add to it, the names will automatically be added to the list in the other sheet. Thanks again