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

  @Override
  @CanIgnoreReturnValue
  @CheckForNull

     * https://github.com/jspecify/checker-framework/issues/8.)
     */
    return removedValue == null ? null : (V) removedValue;
  }

  @Override
  public void addPredecessor(N node, V unused) {
    Object previousValue = adjacentNodeValues.put(node, PRED);
    boolean addedPredecessor;

    if (previousValue == null) {
      addedPredecessor = true;