}

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

    /**
     * @return Optional active project selectors, never {@code null}.
     */

        activation = new ProjectActivation();
        performProjectActivation(
                parser.parse(options, new String[] {"-pl", "test1,+test2,?test3,+?test4"}), activation);
        assertThat(activation.getRequiredActiveProjectSelectors(), containsInAnyOrder("test1", "test2"));
        assertThat(activation.getOptionalActiveProjectSelectors(), containsInAnyOrder("test3", "test4"));

        activation = new ProjectActivation();

        List<MavenProject> result = projects;

        ProjectActivation projectActivation = request.getProjectActivation();
        Set<String> requiredSelectors = projectActivation.getRequiredActiveProjectSelectors();
        Set<String> optionalSelectors = projectActivation.getOptionalActiveProjectSelectors();
        if (!requiredSelectors.isEmpty() || !optionalSelectors.isEmpty()) {

        final Set<String> allOptionalSelectors = new HashSet<>();
        allOptionalSelectors.addAll(projectActivation.getOptionalActiveProjectSelectors());
        allOptionalSelectors.addAll(projectActivation.getRequiredActiveProjectSelectors());
        // We intentionally ignore the results of this method.
        // As a side effect it will log the optional projects that could not be resolved.