private final Object successorValue;

    PredAndSucc(Object successorValue) {
      this.successorValue = successorValue;
    }
  }

  /**
   * A value class representing single connection between the origin node and another node.
   *
   * <p>There can be two types of connections (predecessor and successor), which is represented by
   * the two implementations.
   */
  private abstract static class NodeConnection<N> {