public N adjacentNode(E edge) {
    // We're relying on callers to call this method only with an edge that's in the graph.
    return requireNonNull(incidentEdgeMap.get(edge));
  }

  @Override
  public @Nullable N removeInEdge(E edge, boolean isSelfLoop) {
    if (!isSelfLoop) {
      return removeOutEdge(edge);
    }
    return null;
  }

  @Override
  public N removeOutEdge(E edge) {

      @Override
      public int size() {
        return adjacentNodesMultiset().count(node);
      }
    };
  }

  @Override
  public @Nullable N removeInEdge(E edge, boolean isSelfLoop) {
    if (!isSelfLoop) {
      return removeOutEdge(edge);
    }
    return null;
  }

  @Override
  public N removeOutEdge(E edge) {
    N node = super.removeOutEdge(edge);

    // (We're relying on callers to call this method only with an edge that's in the graph.)
    return requireNonNull(outEdgeMap.get(edge));
  }

  @Override
  public N removeInEdge(E edge, boolean isSelfLoop) {
    if (isSelfLoop) {
      checkNonNegative(--selfLoopCount);
    }
    N previousNode = inEdgeMap.remove(edge);

   *
   * <p>In the undirected case, returns {@code null} if {@code isSelfLoop} is true.
   */
  @CanIgnoreReturnValue
  @Nullable N removeInEdge(E edge, boolean isSelfLoop);

  /** Remove {@code edge} from the set of outgoing edges. Returns the former successor node. */
  @CanIgnoreReturnValue
  N removeOutEdge(E edge);

  /**

    // (We're relying on callers to call this method only with an edge that's in the graph.)
    return requireNonNull(outEdgeMap.get(edge));
  }

  @Override
  public N removeInEdge(E edge, boolean isSelfLoop) {
    if (isSelfLoop) {
      checkNonNegative(--selfLoopCount);
    }
    N previousNode = inEdgeMap.remove(edge);

    N nodeV = connectionsU.adjacentNode(edge);
    NetworkConnections<N, E> connectionsV = requireNonNull(nodeConnections.get(nodeV));
    connectionsU.removeOutEdge(edge);
    connectionsV.removeInEdge(edge, allowsSelfLoops() && nodeU.equals(nodeV));
    edgeToReferenceNode.remove(edge);
    return true;
  }

  private NetworkConnections<N, E> newConnections() {
    return isDirected()