presto-raptor-legacy/src/main/java/io/prestosql/plugin/raptor/legacy/RaptorMetadata.java/RaptorMetadata/DistributionInfo
class RaptorMetadata:        public DistributionInfo(long distributionId, int bucketCount, List<RaptorColumnHandle> bucketColumns)
        {
            this.distributionId = distributionId;
            this.bucketCount = bucketCount;
            this.bucketColumns = ImmutableList.copyOf(requireNonNull(bucketColumns, "bucketColumns is null"));
        }