if tDate.IsZero() {
		return nil
	}
	return e.EncodeElement(tDate.Format(time.RFC3339), startElement)
}

// TransitionDays is a type alias to unmarshal Days in Transition
type TransitionDays int

// UnmarshalXML parses number of days from Transition and validates if
// >= 0
func (tDays *TransitionDays) UnmarshalXML(d *xml.Decoder, startElement xml.StartElement) error {
	var days int
	err := d.DecodeElement(&days, &startElement)

				ID:     "rule-2",
				Status: "Enabled",
				Transition: Transition{
					Days:         TransitionDays(3),
					StorageClass: "TIER-1",
					set:          true,
				},
			},
			{
				ID:     "rule-3",
				Status: "Enabled",
				NoncurrentVersionTransition: NoncurrentVersionTransition{
					NoncurrentDays: TransitionDays(5),
					StorageClass:   "TIER-2",
					set:            true,
				},
			},
		},