I have the following models:

class MyMembership(models.Model):
	_name = "mymembership"         
        _rec_name = "memberid"
    
        memberid = fields.Char(string="Membership ID")    
        member_expiry = fields.Date(string="Expiry Date")​

class MembershipCustomer(models.Model):
        _inherit = "res.partner"
	_inherits = {
            'mymembership': 'partner_member_id',
        }
    	partner_member_id = fields.Many2one('mymembership', ondelete='cascade')

When i edit a partner record and save, there is an error "! The following fields are invalid: Partner Member". I think it forces the user to select a membership record. How do i configure odoo to allow empty partner_membership_id and when there is a membership record selected, the user can clear the partner_membership_id field and save the partner record without any error.