isNotEmpty() is true on empty date field

I have a date field inside a structure which can be left empty. Unfortunately I can’t figure out a way if the field is actually left empty, because the condition
$page->slots()->isNotEmpty() && $page->slots()->toStructure()->first()->time_from()->isNotEmpty()
evaluates as true even if no date is set in the field. Is this a bug? Is there another way?
Many thanks,

Just tested this in a Starterkit and seems to work as expected.

 <?php foreach ($page->social()->toStructure() as $social): ?>
          <?php if($social->date()->isNotEmpty()) {
            echo 'Date is not empty';
          } else {
            echo 'Date is empty';
          } ?>
<?php endforeach ?>

returns “Date is empty” for each item in this case, because all date fields are empty.

Which Kirby version are you using?

I just realized where the problem is, I did a faulty addition of dates and due to insufficient testing assumed the problem was with isNotEmpty(). It wasn’t, everything is working as expected.
I’m sorry for the confusion!