reactor-core/src/main/java/reactor/core/publisher/Mono.java
@Nullable
	public T block() {
		BlockingMonoSubscriber<T> subscriber = new BlockingMonoSubscriber<>();
		Operators.onLastAssembly(this).subscribe(Operators.toCoreSubscriber(subscriber));
		return subscriber.blockingGet();
	}
@Nullable
	public T block() {
		BlockingMonoSubscriber<T> subscriber = new BlockingMonoSubscriber<>();
		Operators.onLastAssembly(this).subscribe(Operators.toCoreSubscriber(subscriber));
		return subscriber.blockingGet();
	}
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