code: @SuppressWarnings("WeakerAccess")
    public CreateInstanceRequest addCluster(
        @Nonnull String clusterId,
        @Nonnull String zone,
        int serveNodes,
        @Nonnull StorageType storageType) {
      CreateClusterRequest clusterRequest =
          CreateClusterRequest.of("ignored-instance-id", clusterId)
              .setZone(zone)
              .setServeNodes(serveNodes)
              .setStorageType(storageType);
      clusterRequests.add(clusterRequest);
  
      return this;
    }
docs: Adds a cluster to the instance request.
  
  <p>All new instances must have at least one cluster. DEVELOPMENT instances must have exactly
  one cluster.
  
  @param clusterId The name of the cluster.
  @param zone The zone where the cluster will be created.
  @param serveNodes The number of nodes that cluster will contain. DEVELOPMENT instance clusters
  must have exactly one node.
  @param storageType The type of storage used by this cluster to serve its parent instance's
  tables.