code: private ContactHeader getContactHeader() throws ParseException {
  		if (contactHeader == null) {
  			final ListeningPoint listeningPoint = sleeSipProvider
  					.getListeningPoint("udp");
  			final javax.sip.address.SipURI sipURI = addressFactory
  					.createSipURI(null, listeningPoint.getIPAddress());
  			sipURI.setPort(listeningPoint.getPort());
  			sipURI.setTransportParam(listeningPoint.getTransport());
  			contactHeader = headerFactory.createContactHeader(addressFactory
  					.createAddress(sipURI));
  		}
  		return contactHeader;
  	}
docs: some helper methods to deal with lazy init of static fields