code: public static <O> Flux<O> error(Throwable throwable, boolean whenRequested) {
  		if (whenRequested) {
  			return onAssembly(new FluxErrorOnRequest<>(throwable));
  		}
  		else {
  			return onAssembly(new FluxError<>(throwable));
  		}
  	}
docs: Create a {@link Flux} that terminates with the specified error, either immediately
  after being subscribed to or after being first requested.
  
  <p>
  <img class="marble" src="doc-files/marbles/errorWhenRequested.svg" alt="">
  
  @param throwable the error to signal to each {@link Subscriber}
  @param whenRequested if true, will onError on the first request instead of subscribe().
  @param <O> the reified type of the target {@link Subscriber}
  
  @return a new failing {@link Flux}