if self.invoice_id.type in ('out_invoice', 'in_invoice'):
            exempt_vat_taxes = self.invoice_line_tax_id.filtered(
                lambda r: not r.amount and r.tax_code_id.type == 'tax' and r.tax_code_id.tax == 'vat')
        else:   # refunds
            exempt_vat_taxes = self.invoice_line_tax_id.filtered(