I'm trying to define some criteria in process builder that checks to see if a user was selected in an Assign to User custom lookup field. However, process builder won't let me select that field for the criteria. I am required to traverse the lookup field and select a field on the user object. Is there a way around that? I just need to check if that field != null. 

[![Set Conditions Screen](https://i.stack.imgur.com/7VhS2.png)](https://i.stack.imgur.com/7VhS2.png)

[![enter image description here](https://i.stack.imgur.com/gmpSd.png)](https://i.stack.imgur.com/gmpSd.png)