docs: public static <IN, OUT> CompletableFuture<OUT> handleAsyncIfNotDone(
  		CompletableFuture<IN> completableFuture,
  		Executor executor,
  		BiFunction<? super IN, Throwable, ? extends OUT> handler) {
  		return completableFuture.isDone() ?
  			completableFuture.handle(handler) :
  			completableFuture.handleAsync(handler, executor);
  	}