}

    private Set<String> getProjectSelectors(final Predicate<ActivationSettings> predicate) {
        return getProjects(predicate).map(activation -> activation.selector).collect(toSet());
    }

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