For MongoDB 3.6 UUID upgrade, the parseCollModUUIDAndNss function allowed an input UUID to not exist in the UUID Catalog if the collMod was empty, since collMod was used to add UUIDs to collections. Instead, parseCollModUUIDAndNss should assert that the UUID (if provided) exists in the catalog because this function is only used during oplog application and there are no replicated UUID upgrade collMods in MongoDB 4.0.