code: public final Mono<T> onErrorMap(Function<? super Throwable, ? extends Throwable> mapper) {
  		return onErrorResume(e -> Mono.error(mapper.apply(e)));
  	}
docs: Transform any error emitted by this {@link Mono} by synchronously applying a function to it.
  <p>
  <img class="marble" src="doc-files/marbles/onErrorMapForMono.svg" alt="">
  
  @param mapper the error transforming {@link Function}
  
  @return a {@link Mono} that transforms source errors to other errors