code: public void setShardAssigner(KinesisShardAssigner shardAssigner) {
  		this.shardAssigner = checkNotNull(shardAssigner, "function can not be null");
  		ClosureCleaner.clean(shardAssigner, true);
  	}
docs: Provide a custom assigner to influence how shards are distributed over subtasks.
  @param shardAssigner shard assigner