docs: private JsonNode processCallbackResponse(final JsonNode resp) {
          if (this.callbackHandler == null) {
              throw new JsiiException("Cannot process callback since callbackHandler was not set");
          }
  
          Callback callback = JsiiObjectMapper.treeToValue(resp.get("callback"), Callback.class);
  
          JsonNode result = null;
          String error = null;
          try {
              result = this.callbackHandler.handleCallback(callback);
          } catch (Exception e) {
              if (e.getCause() instanceof InvocationTargetException) {
                  error = e.getCause().getCause().getMessage();
              } else {
                  error = e.getMessage();
              }
          }
  
          ObjectNode completeResponse = JsonNodeFactory.instance.objectNode();
          completeResponse.put("cbid", callback.getCbid());
          if (error != null) {
              completeResponse.put("err", error);
          }
          if (result != null) {
              completeResponse.set("result", result);
          }
  
          ObjectNode req = JsonNodeFactory.instance.objectNode();
          req.set("complete", completeResponse);
  
          return requestResponse(req);
      }