public B localDc(String localDc) {
    if (localDc == null) throw new NullPointerException("localDc == null");
    this.localDc = localDc;
    return (B) this;
  }
Name of the datacenter that will be considered "local" for latency load balancing. When unset,
load-balancing is round-robin.
zipkin-storage/cassandra/src/main/java/zipkin2/storage/cassandra/CassandraStorageBuilder.java