Alert on a deleted record

Hi!

I have an alert placed via a trigger after a tab fades.

This alert allows me to remind myself that an important field has not been filled in.

But if I delete the record without the field being filled in it happens that:
1) deletion of the record is required. I confirm this. So far, everything is ok.
2) The alert opens that the field has not been filled in. Here is the problem. I expect this alert not to appear.

How can I fix it?

Thank you!