code: public synchronized T getNativeObject(long nativeId) {
      T object = nativeObjToIdMap.get(nativeId);
      if (object != null) {
        return object;
      } else {
        throw new NullPointerException(
            String.format(
                "Could not find object with nativeId: %d. Currently registered ids: %s",
                nativeId, nativeObjToIdMap.keySet()));
      }
    }
docs: Retrieve the native object for given id. Throws if object with that id cannot be found