if !n.set {
		return nil
	}
	if n.StorageClass == "" {
		return errXMLNotWellFormed
	}
	return nil
}

// NextDue returns upcoming NoncurrentVersionTransition date for obj if
// applicable, returns false otherwise.
func (n NoncurrentVersionTransition) NextDue(obj ObjectOpts) (time.Time, bool) {
	if obj.IsLatest || n.StorageClass == "" {
		return time.Time{}, false
	}

	if de.Empty() {
		return nil
	}

	type delMarkerExpiration DelMarkerExpiration
	return enc.EncodeElement(delMarkerExpiration(de), start)
}

// NextDue returns upcoming DelMarkerExpiration date for obj if
// applicable, returns false otherwise.
func (de DelMarkerExpiration) NextDue(obj ObjectOpts) (time.Time, bool) {
	if !obj.IsLatest || !obj.DeleteMarker {
		return time.Time{}, false
	}

}

// IsNull returns true if both date and days fields are null
func (t Transition) IsNull() bool {
	return t.StorageClass == ""
}

// NextDue returns upcoming transition date for obj and true if applicable,
// returns false otherwise.
func (t Transition) NextDue(obj ObjectOpts) (time.Time, bool) {
	if !obj.IsLatest || t.IsNull() {
		return time.Time{}, false
	}

	if !t.IsDateNull() {