in flink-connector-cassandra/src/main/java/org/apache/flink/streaming/connectors/cassandra/CassandraSink.java [345:352]
public CassandraSinkBuilder<IN> setClusterBuilder(ClusterBuilder builder) {
if (this.builder != null) {
throw new IllegalArgumentException(
"Builder was already set. You must use either setHost() or setClusterBuilder().");
}
this.builder = builder;
return this;
}