I have a lookup table that pulls company names from a business address book for a project record. There are instances when there is no applicable company for the particular project. I'd like to have the option to select "Unknown" as the company name. However, I don't want to allow "select on the fly" because of a need for consistency. I could add the company name "Unknown" to the address book but would rather not. Is it possible to create a custom expression for the display field that would pull from the address book and also allow the selection of "Unknown"?
Thanks.