code: public JsonNode handleCallback(final Callback callback) {
  
          if (callback.getInvoke() != null) {
              return invokeCallbackMethod(callback.getInvoke(), callback.getCookie());
          } else if (callback.getGet() != null) {
              return invokeCallbackGet(callback.getGet());
          } else if (callback.getSet() != null) {
              return invokeCallbackSet(callback.getSet());
          }
  
          throw new JsiiException("Unrecognized callback type: get/set/invoke");
      }
docs: Invokes a local callback and returns the result/error.
  @param callback The callback to invoke.
  @return The return value
  @throws JsiiException if the callback failed.