code: @Override
      public void close() {
          System.out.println("closing for " + addOnModel);
          closeCallback.accept(null);
          line.close();
      }
docs: Closes the line, indicating that any system resources
  in use by the line can be released.  If this operation
  succeeds, the line is marked closed and a <code>CLOSE</code> event is dispatched
  to the line's listeners.
  @throws SecurityException if the line cannot be
  closed due to security restrictions.
  
  @see #open
  @see #isOpen