protected void storeID(Hit hit, Execution execution) {
            String id = getProperty(hit, blendingField);

            if (id != null) {
                documentsToStrip.add(id);
            } else {
                if (!result.isFilled(result.getQuery().getPresentation().getSummary())) {
                    fill(result, result.getQuery().getPresentation().getSummary(), execution);
                    id = getProperty(hit, blendingField);
                    if (id != null) {
                        documentsToStrip.add(id);
                    }
                }
            }
        }
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