code: public Object getSession(String id, Protocol protocol) {
  		if(!isValid()) {
  			throw new IllegalStateException("SipApplicationSession already invalidated !");
  		}
  		if(id == null) {
  			throw new NullPointerException("id is null");
  		}
  		if(protocol == null) {
  			throw new NullPointerException("protocol is null");
  		}
  		switch (protocol) {
  			case SIP :
  				return getSipSession(id);
  
  			case HTTP :
  				return findHttpSession(id);
  
  			default :
  				break;
  		}
  		return null;
  	}
docs: {@inheritDoc}