return Collections.emptyList();
  }

  @Override
  <E extends @Nullable Object> Collection<E> unmodifiableCollectionSubclass(
      Collection<E> collection) {
    return Collections.unmodifiableList((List<E>) collection);
  }

  @Override
  Collection<V> wrapCollection(@ParametricNullness K key, Collection<V> collection) {
    return wrapList(key, (List<V>) collection, null);
  }

    return Collections.emptyList();
  }

  @Override
  <E extends @Nullable Object> Collection<E> unmodifiableCollectionSubclass(
      Collection<E> collection) {
    return Collections.unmodifiableList((List<E>) collection);
  }

  @Override
  Collection<V> wrapCollection(@ParametricNullness K key, Collection<V> collection) {
    return wrapList(key, (List<V>) collection, null);
  }

                }

                children.add(new ResolutionNode(a, remoteRepositories, this));
            }
            children = Collections.unmodifiableList(children);
        } else {
            children = Collections.emptyList();
        }
        trail = null;
    }

    /**
     * @return {@link List} < {@link String} > with artifact ids

                .values()
                .stream()
                .map(MavenProject::getVersion)
                .collect(Collectors.collectingAndThen(Collectors.toList(), Collections::unmodifiableList));
        if (!versions.isEmpty()) {
            return versions;
        }
        return getAllProjects()
                .getOrDefault(artifact.getGroupId(), Collections.emptyMap())

    }

    public void setMirroredRepositories(List<ArtifactRepository> mirroredRepositories) {
        if (mirroredRepositories != null) {
            this.mirroredRepositories = Collections.unmodifiableList(mirroredRepositories);
        } else {
            this.mirroredRepositories = Collections.emptyList();
        }
    }

    public boolean isBlocked() {
        return blocked;
    }

    new IteratorTester<T>(
        list.size() * 2 + 2, UNMODIFIABLE, list, IteratorTester.KnownOrder.KNOWN_ORDER) {
      @Override
      protected Iterator<T> newTargetIterator() {
        Iterator<T> iterator = Collections.unmodifiableList(list).iterator();
        return Iterators.peekingIterator(iterator);
      }
    }.test();
  }

  public void testPeekingIteratorBehavesLikeIteratorOnEmptyIterable() {

    }

    public void setMirroredRepositories(List<ArtifactRepository> mirroredRepositories) {
        if (mirroredRepositories != null) {
            this.mirroredRepositories = Collections.unmodifiableList(mirroredRepositories);
        } else {
            this.mirroredRepositories = Collections.emptyList();
        }
    }

    public boolean isBlocked() {
        return blocked;
    }

        this.sortedProjects = sortedProjectLabels.stream()
                .map(id -> projectMap.get(id))
                .collect(Collectors.collectingAndThen(Collectors.toList(), Collections::unmodifiableList));
    }

    @SuppressWarnings("checkstyle:parameternumber")
    private void addEdge(
            Map<String, MavenProject> projectMap,
            Map<String, Map<String, Vertex>> vertexMap,

            value = this.connection.getHeaderField(i);
        }
        for ( Entry<String, List<String>> entry : map.entrySet() ) {
            entry.setValue(Collections.unmodifiableList(entry.getValue()));
        }
        return ( this.headerFields = Collections.unmodifiableMap(map) );
    }


    @Override
    public Map<String, List<String>> getHeaderFields () {

  protected List<E> getOrderedElements() {
    List<E> list = new ArrayList<>();
    for (E e : getSubjectGenerator().order(new ArrayList<E>(getSampleElements()))) {
      list.add(e);
    }
    return Collections.unmodifiableList(list);
  }

  /**
   * @return a suitable location for a null element, to use when initializing containers for tests
   *     that involve a null element being present.
   */