Created attachment 134150 [details] example in calc In Data, Validation (Validez in Spanish), Criteria, Allow List, the "allow empty cells" (Permitir celdas vacias) check, don't work. It's allow deleting this cells with this condition.
Created attachment 134151 [details] pic of data in calc
Created attachment 134152 [details] version of LO 5.0.5.2
Thank you for reporting the bug. it seems you're using an old version of LibreOffice. Could you please try to reproduce it with the latest version of LibreOffice from https://www.libreoffice.org/download/libreoffice-fresh/ ? I have set the bug's status to 'NEEDINFO'. Please change it back to 'UNCONFIRMED' if the bug is still present in the latest version.
I have instaled 5.3.3.2 version and in first time, it's still not working, but i clicked in "allow empty cells" and testing and again clicked in "allow empty cells" in position that is not allow empty cells, and now ITS WORKS :) My coworker still in 5.2.7.2 and to him, this behavior still failing. Maybe this is solutionated in 5.3.3.2 Thanks!!