docs: @Override
      public void upgrade() {
          this.indexSetService.findAll()
              .stream()
              .map(mongoIndexSetFactory::create)
              .flatMap(indexSet -> getReopenedIndices(indexSet).stream())
              .map(indexName -> { LOG.debug("Marking index {} to be reopened using alias.", indexName); return indexName; })
              .forEach(indices::markIndexReopened);
      }