presto-raptor-legacy/src/main/java/io/prestosql/plugin/raptor/legacy/metadata/ShardIterator.java/ShardIterator/getBucketNode
class ShardIterator:    private String getBucketNode(int bucket)
    {
        String node = bucketToNode.get(bucket);
        if (node == null) {
            throw new PrestoException(RAPTOR_ERROR, "No node mapping for bucket: " + bucket);
        }
        return node;
    }