Steps to reproduce:

Fill with in donation form with email address teste®@example.com and push submit

Expected Result:
Email address is shown as invalid

Actual result:
Form is submitted, but validation fails and user sees an empty page.

Notice: Search the application log for Unexpected server-side form validation errors to get ideas for other invalid email addresses.

It seems like the "source" field for the email ConstraintViolation is not set, because the error message Unexpected server-side form validation errors in the application log does not contain the field name and the PHP error log contains notices: PHP Notice: Undefined index: in /usr/share/nginx/www/spenden.wikimedia.de/release-20191111172411/src/Presentation/Presenters/DonationFormViolationPresenter.php on line 146. But this is a side-effect, not the root rause of the underlying error. Please fix it if possible.