static boolean getBoolean( String key, boolean defaultValue ) {
		String value = System.getProperty( key );
		return (value != null) ? Boolean.parseBoolean( value ) : defaultValue;
	}
Checks whether a system property is set and returns {@code true} if its value
is {@code "true"} (case-insensitive), otherwise it returns {@code false}.
If the system property is not set, {@code defaultValue} is returned.
flatlaf-core/src/main/java/com/formdev/flatlaf/FlatSystemProperties.java