Before commit it you want to print original bills with report_original_vendor_bill and that your list contains a refund it ends up with a UserError "You can only print the original document for vendor bills.".
Fixing the filter, using the is_purchase_document helper, allows to properly print documents, including refunds.
closesodoo/odoo#115452
X-original-commit: 7dd553b8ec1bcea8487dfe71c336787f35d69bea
Signed-off-by: Laurent Smet <las@odoo.com>