* enables jsr289 12.5.1 Cloning and Linking
* @return
*/
private SipSession getLinkedSession(SipSessionBase session,
boolean enableFacade) {
SipApplicationSession app = session.getApplicationSession();
SipSessionBase sb = (SipSessionBase) session;
String id = sb.getLinkedSipSessionId();
if (enableFacade && (id == null) && sb.isDerived()) {
// jsr289 support 12.5.1 Cloning and Linking.