NodeConnection(N node) {
      this.node = checkNotNull(node);
    }

    static final class Pred<N> extends NodeConnection<N> {
      Pred(N node) {
        super(node);
      }

      @Override
      public boolean equals(@CheckForNull Object that) {
        if (that instanceof Pred) {
          return this.node.equals(((Pred<?>) that).node);
        } else {
          return false;
        }
      }