public static int nonNegativeHash(Object obj) {
        if (obj == null) {
            return 0;
        }
        int hash = obj.hashCode();
        return hash != Integer.MIN_VALUE ? Math.abs(hash) : 0;
    }
Returns a hash consistent with Spark's Utils.nonNegativeHash().
indexr-query-opt/src/main/java/org/apache/spark/util/JavaUtils.java