code: private static AckEvent unmarshall(ByteBuf json) throws IOException {
          JsonNode jsonNode = Jackson.getObjectMapper().readTree(json.toString(CharsetUtil.UTF_8));
          return UNMARSHALLER.unmarshall(jsonNode);
      }
docs: Unmarshalls the JSON into an {@link AckEvent} object.
  
  @param json JSON data.
  @return AckEvent object.
  @throws IOException If JSON is invalid.