public boolean isFilled(String summaryClass) {
        Set<String> filled = getFilled();
        return (filled == null || filled.contains(summaryClass));
    }
Returns whether all hits in this result have been filled with
the properties contained in the given summary class. Note that
this method will also return true if no hits in this result are
fillable.
container-search/src/main/java/com/yahoo/search/result/HitGroup.java