projectSelector.getRequiredProjectsBySelectors(request, allSortedProjects, requiredSelectors));
            selectedProjects.addAll(
                    projectSelector.getOptionalProjectsBySelectors(request, allSortedProjects, optionalSelectors));

            // it can be empty when an optional project is missing from the reactor, fallback to returning all projects
            if (!selectedProjects.isEmpty()) {

            selectedProjects.addAll(getChildProjects(selectedProject, request));
        }

        return selectedProjects;
    }

    public Set<MavenProject> getOptionalProjectsBySelectors(
            MavenExecutionRequest request, List<MavenProject> projects, Set<String> projectSelectors) {
        Set<MavenProject> resolvedOptionalProjects = new LinkedHashSet<>();

        // We intentionally ignore the results of this method.
        // As a side effect it will log the optional projects that could not be resolved.
        projectSelector.getOptionalProjectsBySelectors(request, session.getAllProjects(), allOptionalSelectors);
    }

    /**
     * Check whether any of the requested optional profiles were not activated or deactivated.
     * @param session the Maven session.