presto-parser/src/main/java/io/prestosql/sql/tree/GroupingSets.java/GroupingSets/GroupingSets
class GroupingSets:    private GroupingSets(Optional<NodeLocation> location, List<List<Expression>> sets)
    {
        super(location);
        requireNonNull(sets, "sets is null");
        checkArgument(!sets.isEmpty(), "grouping sets cannot be empty");
        this.sets = sets.stream().map(ImmutableList::copyOf).collect(toImmutableList());
    }