code: public static <T> ReplayProcessor<T> cacheLastOrDefault(@Nullable T value) {
  		ReplayProcessor<T> b = create(1);
  		if (value != null) {
  			b.onNext(value);
  		}
  		return b;
  	}
docs: Create a {@link ReplayProcessor} that caches the last element it has pushed,
  replaying it to late subscribers. If a {@link Subscriber} comes in <b>before</b>
  any value has been pushed, then the {@code defaultValue} is emitted instead.
  This is a buffer-based ReplayProcessor with a history size of 1.
  <p>
  <img class="marble" src="https://raw.githubusercontent.com/reactor/reactor-core/v3.1.3.RELEASE/src/docs/marble/replaylastd.png"
  alt="">
  
  @param value a default value to start the sequence with in case nothing has been
  cached yet.
  @param <T> the type of the pushed elements
  
  @return a new {@link ReplayProcessor} that replays its last pushed element to each new
  {@link Subscriber}, or a default one if nothing was pushed yet