presto-main/src/main/java/io/prestosql/operator/index/UnloadedIndexKeyRecordSet.java/UnloadedIndexKeyRecordSet/PageAndPositions
class UnloadedIndexKeyRecordSet:        private PageAndPositions(UpdateRequest updateRequest, IntList positions)
        {
            this.updateRequest = requireNonNull(updateRequest, "updateRequest is null");
            this.positions = requireNonNull(positions, "positions is null");
        }