public static int combineHash(Object... objs) {
       int hash = 1;
       for (Object o:objs) {
           hash = 31*hash + (o == null ? 0 : o.hashCode());
       }
       return hash;
    }
Helper method that finds the hashcode for a group of objects.
Inspired by java.util.List
container-search/src/main/java/com/yahoo/search/query/QueryHelper.java