public Boolean parse(final boolean current) {
        for (String s : TOGGLE_VALUES) {
            if (string.equalsIgnoreCase(s)) {
                return !current;
            }
        }
        for (String s : POSITIVE_VALUES) {
            if (string.equalsIgnoreCase(s)) {
                return true;
            }
        }
        for (String s : NEGATIVE_VALUES) {
            if (string.equalsIgnoreCase(s)) {
                return false;
            }
        }
        return null;
    }