ObjectMapper mapper = new ObjectMapper();
/* Looks like NON_DEFAULT can not be used, just because not all
* classes can be instantiated. So for now need to use NON_EMPTY...
*/
mapper.setSerializationInclusion(JsonInclude.Include.NON_EMPTY);
_jsonWriter = mapper.writerWithType(ExternalMetrics.class)
.without(SerializationFeature.FAIL_ON_EMPTY_BEANS);
_entryStore = stores.getEntryStore();
_lastAccessStore = stores.getLastAccessStore();
_metricsProviders = metricsProviders;
}