presto-main/src/main/java/io/prestosql/sql/planner/NodePartitioningManager.java/NodePartitioningManager/getFixedMapping
class NodePartitioningManager:    private static List<InternalNode> getFixedMapping(ConnectorBucketNodeMap connectorBucketNodeMap)
    {
        return connectorBucketNodeMap.getFixedMapping().stream()
                .map(InternalNode.class::cast)
                .collect(toImmutableList());
    }