return getProjectSelectors(pa -> !pa.optional && !pa.active);
    }

    /**
     * @return Optional inactive project selectors, never {@code null}.
     */
    public Set<String> getOptionalInactiveProjectSelectors() {
        return getProjectSelectors(pa -> pa.optional && !pa.active);
    }

    /**
     * Mimics the pre-Maven 4 "selected projects" list.