Table rows are hidden after sorting the Comment column when Office and Comment are empty

Steps to reproduce:

1. Create multiple holiday requests
2. Leave the Office field empty for some of them
3. Accept a request and type a comment
4. Go to the Holiday Request live table
5. Click on the Comment column to sort it Asc or Desc

Expected results: The sorting works as expected.

Actual results: When sorting the Comment column, the entries that have the default value "-" in the Office and Comment columns disappear.