private final boolean isDirected;
  private final boolean allowsSelfLoops;
  private final ElementOrder<N> nodeOrder;

  final MapIteratorCache<N, GraphConnections<N, V>> nodeConnections;

  long edgeCount; // must be updated when edges are added or removed

  /** Constructs a graph with the properties specified in {@code builder}. */
  StandardValueGraph(AbstractGraphBuilder<? super N> builder) {
    this(
        builder,

   * iterable is empty, {@code Optional.absent()} is returned.
   *
   * <p><b>{@code Stream} equivalent:</b> if the goal is to obtain any element, {@link
   * Stream#findAny}; if it must specifically be the <i>first</i> element, {@code Stream#findFirst}.
   *
   * @throws NullPointerException if the first element is null; if this is a possibility, use {@code

   * iterable is empty, {@code Optional.absent()} is returned.
   *
   * <p><b>{@code Stream} equivalent:</b> if the goal is to obtain any element, {@link
   * Stream#findAny}; if it must specifically be the <i>first</i> element, {@code Stream#findFirst}.
   *
   * @throws NullPointerException if the first element is null; if this is a possibility, use {@code