code: @SuppressWarnings("unchecked")
    public static <R> Fallback<R> ofAsync(CheckedConsumer<ExecutionAttemptedEvent<? extends R>> fallback) {
      return new Fallback<>(Functions.fnOf(Assert.notNull((CheckedConsumer) fallback, "fallback")), true);
    }
docs: Configures the {@code fallback} to be executed asynchronously if execution fails. The {@code fallback} accepts an
  {@link ExecutionAttemptedEvent}.
  
  @throws NullPointerException if {@code fallback} is null