docs: private static RuntimeException cancelThrow(ClientCall<?, ?> call, Throwable t) {
      try {
        call.cancel(null, t);
      } catch (Throwable e) {
        assert e instanceof RuntimeException || e instanceof Error;
        logger.log(Level.SEVERE, "RuntimeException encountered while closing call", e);
      }
      if (t instanceof RuntimeException) {
        throw (RuntimeException) t;
      } else if (t instanceof Error) {
        throw (Error) t;
      }
      // should be impossible
      throw new AssertionError(t);
    }