Those are optional fields, certain fields like priceValidUntil
has no value for these products.
Also, some of those fields do exist, if it makes sense for them to be added. For instance, the rating
fields are added if the product has ratings.
That being said, apparently Google violates the spec by not allowing text in the "price" column, so free products currently cause an error. I'll resolve that and look at whether there's any more fields from that list it makes sense to add.