static String toJson(Object o) {
        try {
            return mapper.writeValueAsString(o);
        }
        catch (JsonProcessingException e) {
            throw new RuntimeException(e);
        }
    }
Helper class for generating Vespa search queries
https://docs.vespa.ai/en/reference/query-language-reference.html
client/src/main/java/ai/vespa/client/dsl/Q.java