@Override
		public void paintBorder( Component c, Graphics g, int x, int y, int width, int height ) {
			if( rendererBorder != null )
				rendererBorder.paintBorder( c, g, x, y, width, height );

			// style "mac"
			if( c instanceof JComponent ) {
				Boolean macStyleHint = clientPropertyBooleanStrict( (JComponent) c, KEY_MAC_STYLE_HINT, null );
				if( macStyleHint == Boolean.TRUE ) {
					// paint "checked item" icon
					int ix = c.getComponentOrientation().isLeftToRight()
						? x + scale( padding.left )
						: x + width - scale( padding.right ) - MacCheckedItemIcon.INSTANCE.getIconWidth();
					MacCheckedItemIcon.INSTANCE.paintIcon( c, g, ix, y + ((height - MacCheckedItemIcon.INSTANCE.getIconHeight()) / 2) );
				}
			}
		}
Uninstall border from previously installed component.
Because this border is installed in PopupListCellRenderer.getListCellRendererComponent(),
there is no single place to uninstall it.
This is the reason why this method is called from various places.
flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatComboBoxUI.java