code: public function format(string $question, string $default = null): string {
      if($default != '') {
        $default = sprintf('[%s]', $default);
      }
  
      return trim($question . $default) . sprintf('%s  ', $this->getDelimiter());
    }
docs: If the default is not empty, is appended to the question in square brackets. Both are concatenated, trimmed and the the delmiter is appended with two closing spaces
  
  @param string $question
  @param string $default
  @return string