presto-main/src/main/java/io/prestosql/execution/scheduler/BucketNodeMap.java/BucketNodeMap/BucketNodeMap
class BucketNodeMap:    public BucketNodeMap(ToIntFunction<Split> splitToBucket)
    {
        this.splitToBucket = requireNonNull(splitToBucket, "splitToBucket is null");
    }