In _prepare_merge_orig_links, default value set() is set as default value for created_purchase_line_ids: https://github.com/odoo/odoo/blob/31f134cbdc5fa7a50b88bea7faec682e83cb5fe0/addons/purchase_mrp/models/mrp_production.py#L52 When no data for created_purchase_line_ids, the empty set is not handled: https://github.com/odoo/odoo/blob/31f134cbdc5fa7a50b88bea7faec682e83cb5fe0/addons/purchase_mrp/models/mrp_production.py#L54-L55 However, empty set is not an acceptable value for m2m fields, error will raise in this case. To fix, we replace empty set by empty list. closes odoo/odoo#125994 X-original-commit: 116238c4d832897a407069daec75334bec020cc8 Signed-off-by: William Henrotin (whe) <whe@odoo.com>