code: public final Mono<T> onErrorResume(Function<? super Throwable, ? extends Mono<? extends
  			T>> fallback) {
  		return onAssembly(new MonoOnErrorResume<>(this, fallback));
  	}
docs: Subscribe to a fallback publisher when any error occurs, using a function to
  choose the fallback depending on the error.
  
  <p>
  <img class="marble" src="doc-files/marbles/onErrorResumeForMono.svg" alt="">
  
  @param fallback the function to choose the fallback to an alternative {@link Mono}
  
  @return a {@link Mono} falling back upon source onError
  
  @see Flux#onErrorResume