code: public ServletTimer getTimer(String id) {
  		if(!isValid()) {
  			throw new IllegalStateException("SipApplicationSession already invalidated !");
  		}
  		if(servletTimers != null) {
  			return servletTimers.get(id);
  		}
  		return null;
  	}
docs: /*
  (non-Javadoc)
  @see javax.servlet.sip.SipApplicationSession#getTimer(java.lang.String)