code: public MobicentsSipSession removeSipSession(final MobicentsSipSessionKey key) {
  		if(logger.isDebugEnabled()) {
  			logger.debug("Removing a sip session with the key : " + key);
  		}
  		return sipSessions.remove(key);
  	}
docs: Removes a sip session from the manager by its key
  @param key the identifier for this session
  @return the sip session that had just been removed, null otherwise