presto-raptor-legacy/src/main/java/io/prestosql/plugin/raptor/legacy/metadata/BucketNode.java/BucketNode/BucketNode
class BucketNode:    public BucketNode(int bucketNumber, String nodeIdentifier)
    {
        checkArgument(bucketNumber >= 0, "bucket number must be positive");
        this.bucketNumber = bucketNumber;
        this.nodeIdentifier = requireNonNull(nodeIdentifier, "nodeIdentifier is null");
    }