void put(HitGroup source, Hit hit, Execution execution) {
            if (!hit.isMeta()) {
                if (!known(source, hit, execution)) {
                    addHit(hit);
                }
            } else {
                result.hits().add(hit);
            }
        }
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