public Builder cluster(String cluster) {
            if (!ClickHouseChecker.isNullOrEmpty(cluster)) {
                options.put(PARAM_CLUSTER, cluster);
            } else {
                options.remove(PARAM_CLUSTER);
            }
            return this;
        }
Sets cluster name.

@param cluster cluster name, null means no cluster name
@return this builder
clickhouse-client/src/main/java/com/clickhouse/client/ClickHouseNode.java