I have inherited res.partner and added this the field vendor_code.
the field's been added and I have filled the vendor_code with some values.

classPoPartner(models.Model):
	​_inherit= ['res.partner']
	​vendor_code= fields.Char('Supplier Short Code')


I'm trying to generate a sequence  where it will use the value of the selected field.
but every time it gives company_code as 'None'
here is what it generates: LP/None/2023/7/0000036


classPurhcasePo(models.Model):
	​_name="purchase.po"
	​_description="Purchase PO"


	​#po custom ref generator
	​@api.model
	​defcreate(self, vals):
		​​serial_no=self.env['ir.sequence'].get('purchase.po.customized.sequence')
	​	​company_code=str(vals.get(self.env['res.partner'].browse(vals['partner_id']).vendor_code))
		​​order_type=vals.get('order_type', False)
		​​current_year=str(datetime.datetime.now().year)
		​​current_month=str(datetime.datetime.now().month)
	​	​# merge prefix and serial number
	​	​vals['custom_po_ref'] =order_type+'/'+company_code+'/'+current_year+'/'+current_month+'/'+serial_no
	​	​returnsuper(PurhcasePo, self).create(vals)