code: public static Mono<Void> when(final Iterable<? extends Publisher<?>> sources) {
  		return onAssembly(new MonoWhen(false, sources));
  	}
docs: Aggregate given publishers into a new {@literal Mono} that will be
  fulfilled when all of the given {@literal Publishers} have completed.
  An error will cause pending results to be cancelled and immediate error emission
  to the returned {@link Mono}.
  
  <p>
  <img class="marble" src="doc-files/marbles/when.svg" alt="">
  <p>
  
  @param sources The sources to use.
  
  @return a {@link Mono}.