When adding a extension to a builder it is not being serialized to the message about sdk-java HOT 5 CLOSED

payloadAsString = io.cloudevents.json.Json.encode(cloudEvent);

payloadAsString = io.cloudevents.json.Json.MAPPER.writerFor(CloudEvent.class).writeValueAsString(cloudEvent);

private Map<String, Object> extendedAttributes = new HashMap<>();

  private void resolveExtensions(){
    for (Extension extension : this.getExtensions().orElse(new ArrayList<>())) {
      for (Field field : extension.getClass().getDeclaredFields()) {
        try {
          field.setAccessible(true);
          Object value = field.get(extension);
          extendedAttributes.put(field.getName(), value);
        } catch (IllegalAccessException e) {
          throw new RuntimeException(e);
        }
      }
    }
  }

  @JsonAnyGetter
  public Map<String, Object> getExtendedAttributes() {
    return extendedAttributes;
  }