* all "null" (UNSET).
   *
   * <p>A node with "prev" pointer equal to {@code ENDPOINT} is the first node in the linked list,
   * and a node with "next" pointer equal to {@code ENDPOINT} is the last node.
   */
  @CheckForNull @VisibleForTesting transient long[] links;

  /** Pointer to the first node in the linked list, or {@code ENDPOINT} if there are no entries. */
  private transient int firstEntry;

      // The cast is safe because of the hasLowerBound check.
      E endpoint = uncheckedCastNullableTToT(range.getLowerEndpoint());
      node = root.ceiling(comparator(), endpoint);
      if (node == null) {
        return null;
      }
      if (range.getLowerBoundType() == BoundType.OPEN
          && comparator().compare(endpoint, node.getElement()) == 0) {
        node = node.succ();
      }
    } else {

   * all "null" (UNSET).
   *
   * <p>A node with "prev" pointer equal to {@code ENDPOINT} is the first node in the linked list,
   * and a node with "next" pointer equal to {@code ENDPOINT} is the last node.
   */
  @CheckForNull @VisibleForTesting transient long[] links;

  /** Pointer to the first node in the linked list, or {@code ENDPOINT} if there are no entries. */
  private transient int firstEntry;

    }
    for (N node : subgraph.nodes()) {
      for (N successorNode : graph.successors(node)) {
        if (subgraph.nodes().contains(successorNode)) {
          // requireNonNull is safe because the endpoint pair comes from the graph.
          subgraph.putEdgeValue(
              node,
              successorNode,
              requireNonNull(graph.edgeValueOrDefault(node, successorNode, null)));
        }
      }