presto-main/src/main/java/io/prestosql/sql/planner/RelationPlanner.java/RelationPlanner/getUnnest
class RelationPlanner:    private Optional<Unnest> getUnnest(Relation relation)
    {
        if (relation instanceof AliasedRelation) {
            return getUnnest(((AliasedRelation) relation).getRelation());
        }
        if (relation instanceof Unnest) {
            return Optional.of((Unnest) relation);
        }
        return Optional.empty();
    }