code: @Nullable
  	public T block() {
  		BlockingMonoSubscriber<T> subscriber = new BlockingMonoSubscriber<>();
  		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. Returns that value, or null if the Mono completes empty. In case the Mono
  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/block.svg" alt="">
  <p>
  Note that each block() will trigger a new subscription: in other words, the result
  might miss signal from hot publishers.
  
  @return T the result