public boolean isValid() {

        // check for validity if necessary
        if (validity == NOT_CHECKED) {

            if (existent) {

                if (parseCliValue()) { // parseCliValue has to set value accordingly
                    validity = OK;
                } else {
                    validity = INVALID;
                }
            } else {
                validity = OK;
            }
        }

        // return validity
        if (validity == OK) {
            return true;
        } else {
            return false;
        }
    }