@Override
  public int hashCode() {
    return Objects.hash(
        consumerGroupId,
        creationTime,
        topicNameToSubscribedConsumerIdSet,
        consumerIdToConsumerMeta,
        topicNameToSubscriptionCreationTime);
  }
@return topics subscribed by no consumers in this group after this removal.
@param consumerId if null, remove subscriptions of topics for all consumers
iotdb-core/node-commons/src/main/java/org/apache/iotdb/commons/subscription/meta/consumer/ConsumerGroupMeta.java