code: public final Mono<T> doOnSuccess(Consumer<? super T> onSuccess) {
  		Objects.requireNonNull(onSuccess, "onSuccess");
  		return onAssembly(new MonoPeekTerminal<>(this, onSuccess, null, null));
  	}
docs: Add behavior triggered when the {@link Mono} completes successfully.
  
  <ul>
  <li>null : completed without data</li>
  <li>T: completed with data</li>
  </ul>
  
  <p>
  <img class="marble" src="doc-files/marbles/doOnSuccess.svg" alt="">
  
  @param onSuccess the callback to call on, argument is null if the {@link Mono}
  completes without data
  {@link Subscriber#onNext} or {@link Subscriber#onComplete} without preceding {@link Subscriber#onNext}
  
  @return a new {@link Mono}