code: public static <T> Publisher<T> toPublisher(Completable completable) {
          if (completable == null) {
              throw new NullPointerException("completable");
          }
          return new CompletableAsPublisher<T>(completable);
      }
docs: Converts an RxJava Completable into a Publisher that emits only onError or onComplete.
  @param <T> the target value type
  @param completable the Completable instance to convert
  @return the new Publisher instance
  @since 1.1
  @throws NullPointerException if completable is null