[ADD] stock_invoicing_type

Esto está incorrecto, porque es un id, no es el browse_record. Tendrás que hacer:
```
picking = False
if values.get('picking_id'):
    picking = self.env['stock.picking'].browse(values['picking_id'])
...
    if not picking:
        picking = rec.picking_id
...
    picking.write(...)
```