static Boolean getBooleanStrict( String key, Boolean defaultValue ) {
		String value = System.getProperty( key );
		if( "true".equalsIgnoreCase( value ) )
			return Boolean.TRUE;
		if( "false".equalsIgnoreCase( value ) )
			return Boolean.FALSE;
		return defaultValue;
	}
Checks whether a system property is set and returns {@code Boolean.TRUE} if its value
is {@code "true"} (case-insensitive) or returns {@code Boolean.FALSE} if its value
is {@code "false"} (case-insensitive). Otherwise {@code defaultValue} is returned.
flatlaf-core/src/main/java/com/formdev/flatlaf/FlatSystemProperties.java