docs: @Nullable
      protected final <T> T jsiiAsyncCall(final String method, final Class<T> returnType, @Nullable final Object... args) {
          JsiiClient client = engine.getClient();
          JsiiPromise promise = client.beginAsyncMethod(this.objRef, method, JsiiObjectMapper.valueToTree(args));
  
          engine.processAllPendingCallbacks();
  
          return JsiiObjectMapper.treeToValue(client.endAsyncMethod(promise), returnType);
      }