[PO] Workflow validation by Chef2 if Chef1 is empty

SUGGESTED

Hello,

We are on X3V12, purchase order workflows are working fine for us. We have a validation of "Chef" 1, 2, 3 and 4 depending on the amounts via a affectation rules :

But, for example: if the user's "Chef2" is empty, the workflow fails.

I would like to set the following condition: If "chef2" is empty, then validation.

Thanks