(4, HighZeroBytesDroppedBigSize(*cltv_expiry_height), required),
(8, payment_data, option),
(16, payment_metadata.as_ref().map(|m| WithoutLength(m)), option)
(4, HighZeroBytesDroppedBigSize(*cltv_expiry_height), required),
(8, payment_data, option),
(16, payment_metadata.as_ref().map(|m| WithoutLength(m)), option)