private ZoneId parseExpiryZone(XmlElement expirationTimeEl, FpmlDocument document) { string businessCenter = expirationTimeEl.getChild("businessCenter").Content; Optional <ZoneId> optionalZoneId = document.getZoneId(businessCenter); if (!optionalZoneId.Present) { throw new FpmlParseException("Unknown businessCenter" + " attribute value: " + businessCenter); } return(optionalZoneId.get()); }