presto-raptor-legacy/src/main/java/io/prestosql/plugin/raptor/legacy/metadata/BucketReassigner.java/BucketReassigner/BucketReassigner
class BucketReassigner:    public BucketReassigner(Set<String> activeNodes, List<BucketNode> bucketNodes)
    {
        checkArgument(!activeNodes.isEmpty(), "activeNodes must not be empty");
        this.activeNodes = ImmutableList.copyOf(requireNonNull(activeNodes, "activeNodes is null"));
        this.bucketNodes = requireNonNull(bucketNodes, "bucketNodes is null");
    }