return waitFor(closingFunction, ClosingFunction.class);
    }

    @SuppressWarnings("unchecked") // proxy for a generic class
    <T, U> AsyncClosingFunction<T, U> waitFor(AsyncClosingFunction<T, U> asyncClosingFunction) {
      return waitFor(asyncClosingFunction, AsyncClosingFunction.class);
    }

    @SuppressWarnings("unchecked") // proxy for a generic class