code: public static <T> Action1<Notification<T>> split(
          @Nullable Action1<T> onNext) {
  
          return split(onNext, null);
      }
docs: Returns an {@link Action1} which can be used to split a {@link Notification} into appropriate
  dematerialized onNext calls.
  
  @param onNext a method that will be called in case of onNext notification, or null.
  @param <T>    a type of onNext values.
  @return an {@link Action1} that can be used to split a {@link Notification} into appropriate
  onNext calls.