void mergeResults(List<HitGroup> groups, Execution execution) {
            // note, different loop direction from scanResult()
            for(HitGroup group : groups.subList(1, groups.size())) {
                for(Hit hit : group.asList()) {
                    if (hit.isMeta()) {
                        result.hits().add(hit);
                    } else {
                        put(group, hit, execution);
                    }
                }
            }
        }
Produce a single blended hit list from a group of hitgroups.

This assumes that all hits are organized into hitgroups. If not, blending will not be performed.
container-search/src/main/java/com/yahoo/prelude/searcher/BlendingSearcher.java