public function asDateTime($key, $format = NULL)
{
$time = $this[$key];
if (!$time instanceof DateTime) {
if (!$time || substr((string) $time, 0, 3) === '000') {
// '', NULL, FALSE, '0000-00-00', ...
return NULL;
}
$time = new DateTime($time);
}
return $format === NULL ? $time : $time->format($format);
}