code: public AckEvent unmarshall(JsonNode json) {
          return new AckEvent()
              .withFragmentNumber(getTextField(json, FRAGMENT_NUMBER))
              .withFragmentTimecode(getLongField(json, FRAGMENT_TIMECODE))
              .withAckEventType(AckEventType.of(getTextField(json, ACK_EVENT_TYPE)))
              .withErrorCode(getTextField(json, ERROR_CODE))
              .withErrorId(getIntegerField(json, ERROR_ID));
      }
docs: Unmarshalls the given JSON into an {@link AckEvent} object.
  
  @param json JSON document.
  @return {@link AckEvent} object.