Set Owner Id to null with business rules

Hi,

I'm trying to set the Owner Id to null when creating a record from a custom entity.

I'm using condition: If CretaedOn does not contain data

and action is: Set Owner Id to Modified by

as I suppose Modified by does not contain data either.

This doesn't work as it it, but if I change the action to set up a date time field, it works.

Any trick to do this with a business unit rule? If so, I'm thinning JS would be any remaining option?