This patch reproduces what we did for `to_api_mapping`: make it always
present on Koha::Object classes. This has the side-effect of... making
things more secure!
Before this patch, if undefined, all attributes were returned.
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io> Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com> Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com> Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>