how to set apns-expiration as 0 (zero)?

[deltapath-eric]

https://developer.apple.com/documentation/usernotifications/setting_up_a_remote_notification_server/sending_notification_requests_to_apns/

The date at which the notification is no longer valid. This value is a UNIX epoch expressed in seconds (UTC). If the value is nonzero, APNs stores the notification and tries to deliver it at least once, repeating the attempt as needed until the specified date. If the value is 0, APNs attempts to deliver the notification only once and doesn’t store it.

if i understand correctly, the value can be 0 which make the notification will not resend

at client.go

if !n.Expiration.IsZero() {
  r.Header.Set("apns-expiration", fmt.Sprintf("%v", n.Expiration.Unix()))
}

seem if the value isZero(), the header will not be set and there is not way to set the header as 0

please correct me if i am wrong, thanks!