ATTN! The following code produces different result in PHP 7 and PHP 8!

gmdate('Y-m-d\TH:i:s', null);

In PHP 7 null in gmdate('Y-m-d\TH:i:s', null) translated as 0, although gmdate('Y-m-d\TH:i:s'); (w/o 2nd parameter specified) works as it should.

This issue is fixed in PHP 8.