Webform element preview serialize() error

Here is a patch to at least fix the error, would be nice to have a preview though.

Try this:
$office_hours = self::serialize($office_hours ?? []);
That will turn NULL into an empty array, and the lst line will be executed, too.

I cannot reproduce your error. I found the 'preview' setting, and tested it with a webform with empty office_hours.
the input is an array with 14 empty slots (7*2)
the output of 'serialize' is an empty array.

So, on my side, there is no error.

P.S. It seems the new exceptions and seasons feature is not copied into WebformElement.

P.S. new release 8.x-1.12 is now published. Please test.

Will test as soon as I can.

Can confirm that latest fixes this, can be closed.

Nice.
P.S. Please check a new open issue, regarding Exceptions

FYI, please check the related issue 🐛 Webform element preview serialize() error in Build mode Fixed