public void add(int index, Hit hit) {
        if (hit instanceof ErrorHit) { // Merge instead
            add(hit);
            return;
        }

        boolean wasSorted = hitsSorted;
        handleNewHit(hit);
        hits.add(index, hit);
        hitsSorted = wasSorted;
    }
Adds a hit to this group in the specified index,
all existing hits on this index and higher will have their index increased by one.

<b>Note:</b> If the group was sorted, it will still be considered sorted after this call.
container-search/src/main/java/com/yahoo/search/result/HitGroup.java