Model target,
            List<? extends DependencyManagement> sources,
            ModelBuilderRequest request,
            ModelProblemCollector problems) {
        if (sources != null && !sources.isEmpty()) {
            Map<String, Dependency> dependencies = new LinkedHashMap<>();

            DependencyManagement depMgmt = target.getDependencyManagement();

            if (depMgmt != null) {

     *
     * So {@code (b : c).plus(a) == (a : b : c)}
     */
    @CheckReturnValue
    public abstract PersistentList<T> plus(T element);

    public abstract boolean isEmpty();

    private PersistentList() {}

    private static final PersistentList<Object> NIL = new PersistentList<Object>() {
        @Override
        public void forEach(Consumer<? super Object> consumer) {
        }

            // The file pom may not contain the modelVersion yet, as it may be set later by the
            // ModelVersionXMLFilter.
            if (m.getModelVersion() != null && !m.getModelVersion().isEmpty()) {
                validateModelVersion(problems, m.getModelVersion(), m, VALID_MODEL_VERSIONS);
            }

            validateStringNoExpression("groupId", problems, Severity.WARNING, Version.V20, m.getGroupId(), m);

            .collect(Collectors.toList());

        StyledTextOutput styledTextOutput = getRenderer().getTextOutput();
        if (!softwareTypes.isEmpty()) {
            renderSectionTitle("Available software types");
            styledTextOutput.println();

            softwareTypes.forEach(type -> {

    Optional<Object> getOptional() {
      if (extras.isEmpty()) {
        return Optional.ofNullable(element);
      } else {
        throw multiples(false);
      }
    }

    Object getElement() {
      if (element == null) {
        throw new NoSuchElementException();
      } else if (extras.isEmpty()) {
        return element;
      } else {
        throw multiples(false);

        }
    }

    @Override
    public synchronized Throwable getCause() {
        if (hideCause.get()) {
            return null;
        }
        return causes.isEmpty() ? null : causes.get(0);
    }

    @SuppressWarnings("DefaultCharset")
    @Override
    public void printStackTrace(PrintStream printStream) {
        PrintWriter writer = new PrintWriter(printStream);

    if (ranges.isEmpty()) {
      return ImmutableMap.of();
    }
    RegularImmutableSortedSet<Range<K>> rangeSet =
        new RegularImmutableSortedSet<>(ranges, Range.<K>rangeLexOrdering());
    return new ImmutableSortedMap<>(rangeSet, values);
  }

  @Override
  public ImmutableMap<Range<K>, V> asDescendingMapOfRanges() {
    if (ranges.isEmpty()) {
      return ImmutableMap.of();
    }

                if (dependency.getGroupId() == null
                        || dependency.getGroupId().isEmpty()
                        || dependency.getArtifactId() == null
                        || dependency.getArtifactId().isEmpty()
                        || dependency.getVersion() == null
                        || dependency.getVersion().isEmpty()) {
                    // guard against case where best-effort resolution for invalid models is requested

                profileSelector.getActiveProfiles(request.getProfiles(), profileActivationContext, problems);

        result.setActiveExternalProfiles(activeExternalProfiles);

        if (!activeExternalProfiles.isEmpty()) {
            Properties profileProps = new Properties();
            for (Profile profile : activeExternalProfiles) {
                profileProps.putAll(profile.getProperties());
            }

            Model target,
            List<? extends DependencyManagement> sources,
            ModelBuildingRequest request,
            ModelProblemCollector problems) {
        if (sources != null && !sources.isEmpty()) {
            Map<String, Dependency> dependencies = new LinkedHashMap<>();

            DependencyManagement depMgmt = target.getDependencyManagement();

            if (depMgmt != null) {