* months and days always start with 1.
*/
if (substr($s, 0, 10) <= '0001-01-01') {
+ if ($s < '0000-00-00') {
+ $s = '0000-00-00';
+ }
$d = new DateTime($s . ' + 32 days', new DateTimeZone('UTC'));
return str_replace('1', '0', $d->format($format));
}