public static void registerCustomDefaultsSource( File folder ) {
		if( customDefaultsSources == null )
			customDefaultsSources = new ArrayList<>();
		customDefaultsSources.add( folder );
	}
Registers a folder where FlatLaf searches for properties files with custom UI defaults.
<p>
See {@link #registerCustomDefaultsSource(String)} for details.

@param folder a folder
flatlaf-core/src/main/java/com/formdev/flatlaf/FlatLaf.java