return adjacentNodeValues.remove(node);
  }

  @Override
  public void addPredecessor(N node, V value) {
    @SuppressWarnings("unused")
    V unused = addSuccessor(node, value);
  }

  @Override
  public @Nullable V addSuccessor(N node, V value) {
    return adjacentNodeValues.put(node, value);
  }

   * becomes a predecessor. Associates {@code value} with the edge connecting the two nodes. Returns
   * the value previously associated with the edge connecting the two nodes.
   */
  @CanIgnoreReturnValue
  @Nullable V addSuccessor(N node, V value);

      if (orderedNodeConnections != null) {
        orderedNodeConnections.add(new NodeConnection.Pred<>(node));
      }
    }
  }

  @SuppressWarnings("unchecked")
  @Override
  public @Nullable V addSuccessor(N node, V value) {
    Object previousValue = adjacentNodeValues.put(node, value);
    Object previousSuccessor;

    if (previousValue == null) {
      previousSuccessor = null;

    }

    GraphConnections<N, V> connectionsU = nodeConnections.get(nodeU);
    if (connectionsU == null) {
      connectionsU = addNodeInternal(nodeU);
    }
    V previousValue = connectionsU.addSuccessor(nodeV, value);
    GraphConnections<N, V> connectionsV = nodeConnections.get(nodeV);
    if (connectionsV == null) {
      connectionsV = addNodeInternal(nodeV);
    }
    connectionsV.addPredecessor(nodeU, value);