I made a related field that takes the information from purchase orders to the stock picking. I want to make that if the field is empty, in stock picking let the users edit that field.

from odoo import fields, models, api class Picking(models.Model): _inherit = 'stock.picking' analytic_account_id = fields.Many2one( string='Project', related='purchase_id.analytic_account_id', store=True, readonly=False) ​

Thats what I have. What should I add?