@Override
    ObjectNode toJson(ObjectMapper mapper) {
      ObjectNode result = mapper.createObjectNode();
      result.with("constant_score").set("filter", builder.toJson(mapper));
      return result;
    }
A query that wraps a filter and simply returns a constant score equal to the
query boost for every document in the filter.
criteria/elasticsearch/src/org/immutables/criteria/elasticsearch/QueryBuilders.java