return waitFor(asyncClosingCallable, AsyncClosingCallable.class);
    }

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

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