DateTime Mapper always defaults to "now" when submission has empty value

Problem/Motivation

When mapping a webform datetime field to a DrupalDateTime field, the mapper treats empty strings as "now".

Proposed resolution

Treat empty values as NULL. I guess the problem is this line here:

https://git.drupalcode.org/project/webform_content_creator/-/blob/4.x/sr...

$datetime = new DrupalDateTime('', 'UTC');

$datetime will be always "now".