presto-raptor-legacy/src/main/java/io/prestosql/plugin/raptor/legacy/storage/BucketBalancer.java/ClusterState/ClusterState
class ClusterState:        public ClusterState(
                Set<String> activeNodes,
                Map<String, Long> assignedBytes,
                Multimap<Distribution, BucketAssignment> distributionAssignments,
                Map<Distribution, Long> distributionBucketSize)
        {
            this.activeNodes = ImmutableSet.copyOf(requireNonNull(activeNodes, "activeNodes is null"));
            this.assignedBytes = ImmutableMap.copyOf(requireNonNull(assignedBytes, "assignedBytes is null"));
            this.distributionAssignments = ImmutableMultimap.copyOf(requireNonNull(distributionAssignments, "distributionAssignments is null"));
            this.distributionBucketSize = ImmutableMap.copyOf(requireNonNull(distributionBucketSize, "distributionBucketSize is null"));
        }