Registration date empty in email notification to first person on waiting list

One-sentence description

In the (Dutch) email sent to the first person on the waiting list when someone cancels their registration, the registration date is empty, resulting in the message "Je hebt je op aangemeld voor...".

Current behaviour / Reproducing the bug

1. Be the first on the waiting list for a certain event.
2. Trick someone into cancelling their registration so you can go to the event.
3. Receive an email notifying you that you can attend the event.
4. Notice your registration date is not included in the email.

Expected behaviour

The registration date is not empty.