@Override
  public boolean equals(Object o) {
    if (this == o) {
      return true;
    }
    if (o == null || getClass() != o.getClass()) {
      return false;
    }
    Pair<?, ?> pair = (Pair<?, ?>) o;
    if (!Objects.equals(first, pair.first)) {
      return false;
    }
    return Objects.equals(second, pair.second);
  }
@return the second object in the pair.
ambry-utils/src/main/java/com/github/ambry/utils/Pair.java