@Override
			public void actionPerformed( ActionEvent e ) {
				if( timer != null && !isDisplayable() ) {
					timer.stop();
					return;
				}

				scroll( direction == SwingConstants.NORTH ? -1 : 1 );
			}
Scroll when user presses Up or Down keys.
flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatPopupMenuUI.java