public static boolean hasGroupingList(Query query) {
        Object obj = query.properties().get(PROP_GROUPINGLIST);
        return (obj instanceof List);
    }
Returns the list of {@link Grouping} objects assigned to the given query. If no list has been assigned, this
method returns an empty list.

@param query the query whose grouping list to return
@return the list of assigned grouping objects
container-search/src/main/java/com/yahoo/search/grouping/vespa/GroupingExecutor.java