code: public final Mono<Void> and(Publisher<?> other) {
  		if (this instanceof MonoWhen) {
  			@SuppressWarnings("unchecked") MonoWhen o = (MonoWhen) this;
  			Mono<Void> result = o.whenAdditionalSource(other);
  			if (result != null) {
  				return result;
  			}
  		}
  
  		return when(this, other);
  	}
docs: Join the termination signals from this mono and another source into the returned
  void mono
  
  <p>
  <img class="marble" src="doc-files/marbles/and.svg" alt="">
  <p>
  @param other the {@link Publisher} to wait for
  complete
  @return a new combined Mono
  @see #when