@Override
	public void update( Graphics g, JComponent c ) {
		// fill background if opaque to avoid garbage if user sets opaque to true
		if( c.isOpaque() )
			FlatUIUtils.paintParentBackground( g, c );

		if( isHelpButton( c ) ) {
			helpButtonIcon.paintIcon( c, g, 0, 0 );
			return;
		}

		if( isContentAreaFilled( c ) )
			paintBackground( g, c );

		paint( g, c );
	}
Returns true if the button has an icon but no text,
or it does not have an icon and the text is either "..." or one character.
flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatButtonUI.java