return null == topologicallySortedProjects
                ? Collections.emptyList()
                : Collections.unmodifiableList(topologicallySortedProjects);
    }

    public DependencyResolutionResult getDependencyResolutionResult() {
        return dependencyResolutionResult;
    }

    public MavenExecutionResult setDependencyResolutionResult(DependencyResolutionResult dependencyResolutionResult) {

     */
    List<MavenProject> getTopologicallySortedProjects();

    MavenExecutionResult setDependencyResolutionResult(DependencyResolutionResult result);

    DependencyResolutionResult getDependencyResolutionResult();

    // for each exception
    // - knowing what artifacts are missing
    // - project building exception
    // - invalid project model exception: list of markers
    // - xmlpull parser exception

                @Nonnull
                @Override
                public Optional<DependencyResolverResult> getDependencyResolverResult() {
                    return Optional.ofNullable(res.getDependencyResolutionResult())
                            .map(r -> new DefaultDependencyResolverResult(
                                    null, r.getCollectionErrors(), session.getNode(r.getDependencyGraph()), 0));
                }