code: @Override
    public String select(final int index) {
      checkIsInMultiOrPipeline();
      client.select(index);
      String statusCodeReply = client.getStatusCodeReply();
      client.setDb(index);
  
      return statusCodeReply;
    }
docs: Select the DB with having the specified zero-based numeric index. For default every new client
  connection is automatically selected to DB 0.
  @param index
  @return Status code reply