query_objects filters and sort silently skip objects with no stored row for the field

Filters and sort are compiled as an inner join on the property row, so an object that has no stored row for the field (created through write_object without that field, or the field was added to the class after the object was saved) never matches a filter on it, not even !=, and never appears in a sort on it. A stored empty value is included and sorts wherever the database orders nulls.