'(empty)' filter option on some Live Data columns doesn't work as expected

Steps to reproduce

1. Go to a page
2. Click on Attachments tab
3. Upload some files (optional: of different sizes)
4. On 'File size' column, click on drop-down and select '(empty)' option
5. Observe the filtered entries

Expected results

No entries should be displayed, since all attachments have a certain size (and maybe the 'empty' option should not be available in this case).

Actual results

All entries are displayed back on the table.

I've set XWiki 14.10.21 as the Affects Version since that was the oldest version tested, but the issue is older.