code: public function getDateTime($keys, DateTime $default = null)
      {
          $value = $this->getString($keys);
          if (empty($value)) {
              $result = $default;
          } elseif ($value === (string)(int)$value) {
              $result = new DateTime();
              $result->setTimestamp((int)$value);
          } else {
              $result = new DateTime($value);
          }
          return $result;
      }
docs: Returns a DateTime instance from the data container. A string value is interpreted as date string, an integer
  value is interpreted as UNIX timestamp.
  @param string|string[] $keys
  @param DateTime|null $default
  @return DateTime|null