private void addZeroConstraintPostingList(ArrayList<PostingList> postingLists) {
            if (zeroConstraintDocuments.length > 0) {
                postingLists.add(new ZeroConstraintPostingList(zeroConstraintDocuments));
            }
        }
Retrieves a stream of hits for the given query.

@param query Specifies the boolean variables that are true.
@return A stream of hits.
predicate-search/src/main/java/com/yahoo/search/predicate/PredicateIndex.java