code: public function doDefaultValueConversionByType($value, $type, array $record) {
          switch ($type) {
              case static::TYPE_DATETIME:
                  return date(static::FORMAT_DATETIME, is_numeric($value) ? $value : strtotime($value));
              case static::TYPE_DATE:
                  return date(static::FORMAT_DATE, is_numeric($value) ? $value : strtotime($value));
              case static::TYPE_TIME:
                  return date(static::FORMAT_TIME, is_numeric($value) ? $value : strtotime($value));
              case static::TYPE_MULTILINE:
                  return '<pre class="multiline-text">' . $value . '</pre>';
              case static::TYPE_JSON:
              case static::TYPE_JSONB:
                  if (!is_array($value) && $value !== null) {
                      if (is_string($value) || is_numeric($value) || is_bool($value)) {
                          $value = json_decode($value, true);
                          if ($value === null && strtolower($value) !== 'null') {
                              $value = 'Failed to decode JSON: ' . print_r($value, true);
                          }
                      } else {
                          $value = 'Invalid value for JSON: ' . print_r($value, true);
                      }
                  }
                  return '<pre class="json-text">'
                          . htmlentities(stripslashes(json_encode($value, JSON_PRETTY_PRINT | JSON_UNESCAPED_UNICODE)))
                      . '</pre>';
                  break;
          }
          return $value;
      }
docs: Default value converter by value type
  @param mixed $value
  @param string $type - one of static::TYPE_*
  @param array $record
  @return mixed