code: @NonNull
      @CheckResult
      @Override
      public Single<Optional<T>> asRxSingle() {
          return RxJavaUtils.createSingleOptional(storIOContentResolver, this);
      }
docs: Creates {@link Single} which will perform Get Operation lazily when somebody subscribes to it and send result to observer.
  <dl>
  <dt><b>Scheduler:</b></dt>
  <dd>Operates on {@link StorIOContentResolver#defaultRxScheduler()} if not {@code null}.</dd>
  </dl>
  
  @return non-null {@link Single} which will perform Get Operation.
  And send result to observer.