code: public static <T> Mono<T> fromFuture(Supplier<? extends CompletableFuture<? extends T>> futureSupplier) {
  		return defer(() -> onAssembly(new MonoCompletionStage<>(futureSupplier.get())));
  	}
docs: Create a {@link Mono} that wraps a {@link CompletableFuture} on subscription,
  emitting the value produced by the Future.
  
  <p>
  <img class="marble" src="doc-files/marbles/fromFutureSupplier.svg" alt="">
  <p>
  Note that the future is not cancelled when that Mono is cancelled, but that behavior
  can be obtained by using a {@link #doFinally(Consumer)} that checks
  for a {@link SignalType#CANCEL} and calls {@link CompletableFuture#cancel(boolean)}.
  
  @param futureSupplier The {@link Supplier} of a {@link CompletableFuture} that will produce a value (or a null to
  complete immediately). This allows lazy triggering of future-based APIs.
  @param <T> type of the expected value
  @return A {@link Mono}.
  @see #fromCompletionStage(Supplier) fromCompletionStage for a generalization