}
    return (V) value;
  }

  @Override
  public void removePredecessor(N node) {
    checkNotNull(node);

    Object previousValue = adjacentNodeValues.get(node);
    boolean removedPredecessor;

    if (previousValue == PRED) {
      adjacentNodeValues.remove(node);
      removedPredecessor = true;
    } else if (previousValue instanceof PredAndSucc) {

    }
    return (V) value;
  }

  @Override
  public void removePredecessor(N node) {
    checkNotNull(node);

    Object previousValue = adjacentNodeValues.get(node);
    boolean removedPredecessor;

    if (previousValue == PRED) {
      adjacentNodeValues.remove(node);
      removedPredecessor = true;
    } else if (previousValue instanceof PredAndSucc) {