reactor-core/src/main/java/reactor/core/publisher/BlockingSingleSubscriber.java
@Nullable
	final T blockingGet(long timeout, TimeUnit unit) {
		if (Schedulers.isInNonBlockingThread()) {
			throw new IllegalStateException("block()/blockFirst()/blockLast() are blocking, which is not supported in thread " + Thread.currentThread().getName());
		}
		if (getCount() != 0) {
			try {
				if (!await(timeout, unit)) {
					dispose();
					throw new IllegalStateException("Timeout on blocking read for " + timeout + " " + unit);
				}
			}
			catch (InterruptedException ex) {
				dispose();
				RuntimeException re = Exceptions.propagate(ex);
				//this is ok, as re is always a new non-singleton instance
				re.addSuppressed(new Exception("#block has been interrupted"));
				throw re;
			}
		}

		Throwable e = error;
		if (e != null) {
			RuntimeException re = Exceptions.propagate(e);
			//this is ok, as re is always a new non-singleton instance
			re.addSuppressed(new Exception("#block terminated with an error"));
			throw re;
		}
		return value;
	}
@Nullable
	final T blockingGet(long timeout, TimeUnit unit) {
		if (Schedulers.isInNonBlockingThread()) {
			throw new IllegalStateException("block()/blockFirst()/blockLast() are blocking, which is not supported in thread " + Thread.currentThread().getName());
		}
		if (getCount() != 0) {
			try {
				if (!await(timeout, unit)) {
					dispose();
					throw new IllegalStateException("Timeout on blocking read for " + timeout + " " + unit);
				}
			}
			catch (InterruptedException ex) {
				dispose();
				RuntimeException re = Exceptions.propagate(ex);
				//this is ok, as re is always a new non-singleton instance
				re.addSuppressed(new Exception("#block has been interrupted"));
				throw re;
			}
		}

		Throwable e = error;
		if (e != null) {
			RuntimeException re = Exceptions.propagate(e);
			//this is ok, as re is always a new non-singleton instance
			re.addSuppressed(new Exception("#block terminated with an error"));
			throw re;
		}
		return value;
	}
Block until the first value arrives and return it, otherwise
return null for an empty source and rethrow any exception.

@param timeout the timeout to wait
@param unit the time unit

@return the first value or null if the source is empty