Each product is assigned a catalog, whether they have Upsells or not.
WITH YOUR FIRST SET OF CODE:
Products that have Upsells:
string(80) “http://domainname.com/wp-content/uploads/Fire-Catalog.pdf”
Products that have no Upsells are blank
WITH YOUR SECOND SET OF CODE:
Products that have Upsells:
string(80) “http://domainname.com/wp-content/uploads/Fire-Catalog.pdf”
Products that have no Upsells are blank