static String getButtonTypeStr( AbstractButton c ) {
		// get from client property
		Object value = c.getClientProperty( BUTTON_TYPE );
		if( value instanceof String )
			return (String) value;

		// get from styling property
		ButtonUI ui = c.getUI();
		return (ui instanceof FlatButtonUI) ? ((FlatButtonUI)ui).buttonType : null;
	}
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