Setting priority as NULL within business process

[Jon Green]

Is it possible to set the priority as NULL within a business process?

Background: We are configuring our company portal to enable most customers to self help through guidance within process captures, when the user enters that they have solved the issue a request is created and solved in the business process. All self help requests have a low priority set on resolution, however if the user reopens the request either through the portal or via an email response I would like the priority to be reviewed, so reset to null and focus set. Unfortunately I get an error within the business process where the process in the automation is blank. Any ideas welcome.

Thanks

Jon