code: public static @NonNull CompletableExecutorService completableDecorator(final @NonNull ExecutorService executorService) {
      if(executorService instanceof CompletableExecutorService) {
        return (CompletableExecutorService) executorService;
      }
      return new CompletableDecorator(executorService);
    }
docs: Creates an {@link ExecutorService} whose {@code submit} and {@code invokeAll} methods submit
  {@link RunnableCompletableFuture} instances to the given delegate executor.
  
  @param executorService the executor service
  @return a completable executor service