Can you Filter formula fields from CX Sales integration Import?

I've attempted to filter a formula field from CX Sales into Eloqua but none of the following filters work to import a record with the field not NULL

PersonDEO_MemberOf_c != ''

PersonDEO_MemberOf_c != “”

PersonDEO_MemberOf_c is not null

PersonDEO_MemberOf_c != "null"

I've referred to this document but it does not present a solution for this:

Has anyone found a solution?