presto-main/src/main/java/io/prestosql/operator/BucketPartitionFunction.java/BucketPartitionFunction/BucketPartitionFunction
class BucketPartitionFunction:    public BucketPartitionFunction(BucketFunction bucketFunction, int[] bucketToPartition)
    {
        this.bucketFunction = requireNonNull(bucketFunction, "bucketFunction is null");
        this.bucketToPartition = requireNonNull(bucketToPartition, "bucketToPartition is null").clone();
        partitionCount = IntStream.of(bucketToPartition).max().getAsInt() + 1;
    }