code: public Optional<T> blockOptional() {
  		BlockingOptionalMonoSubscriber<T> subscriber = new BlockingOptionalMonoSubscriber<>();
  		Operators.onLastAssembly(this).subscribe(Operators.toCoreSubscriber(subscriber));
  		return subscriber.blockingGet();
  	}
docs: Subscribe to this {@link Mono} and <strong>block indefinitely</strong> until a next signal is
  received or the Mono completes empty. Returns an {@link Optional}, which can be used
  to replace the empty case with an Exception via {@link Optional#orElseThrow(Supplier)}.
  In case the Mono itself errors, the original exception is thrown (wrapped in a
  {@link RuntimeException} if it was a checked exception).
  
  <p>
  <img class="marble" src="doc-files/marbles/blockOptional.svg" alt="">
  <p>
  Note that each blockOptional() will trigger a new subscription: in other words, the result
  might miss signal from hot publishers.
  
  @return T the result