Handle 'notify' field issue upon creating fee/fine

Expected behavior:
1. On folio-testing as diku_admin;
2. Make the preliminary steps in order to create a fee/fine (create owner, payment method, manual charge);
3. Checkout a loan and navigate to the open loans tab;
4. Open an action dropdown for the open loan and choose "New fee/fine";
5. Fill all required fields in the appeared modal and click "Chare & pay now" button and then hit the "Confirm" button in the confirm dialog:

Expected behavior: Fee/fine created and no error modal appeared;
Actual behavior: Fee/fine is not created and no error modal appeared (see Error.png in attachments);