code: public void addNamingObjectListener(NamingObjectListener nol) {
          if (nol == null)
              throw new IllegalArgumentException("The NameingObjectListener must not be null");
  
          ArrayList listener = getListener();
  
          synchronized(listener) {
              if (listener.contains(nol))
                  return;
              listener.add(nol);
          }
      }
docs: This method will add a <code>NamingObjectListener</code> to the set of listeners for the NamingObject event.
  @param nol The <code>NamingObjectListener</code> to add as a listener.  This must not be null.
  @throws IllegalArgumentException when nol is null.