JsonService() {
        SimpleModule module = new SimpleModule("cats", new Version(1, 0, 0, null));
        module.addSerializer(GString.class, ToStringSerializer.instance);
        mapper.registerModule(module)

        mapper.configure(SerializationConfig.Feature.WRITE_NULL_PROPERTIES, false)
        mapper.configure(SerializationConfig.Feature.WRITE_NULL_MAP_VALUES, false)
        mapper.configure(SerializationConfig.Feature.WRITE_EMPTY_JSON_ARRAYS, false)
        mapper.configure(SerializationConfig.Feature.WRITE_DATES_AS_TIMESTAMPS, false)
        mapper.configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES, false)

        DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSZ");
        dateFormat.setTimeZone(TimeZone.getTimeZone("UTC"));
        mapper.setDateFormat(dateFormat)
    }