[#4069] Fix crash when using some registration backends #11726

Job	Run time
Set up docker build 'dynamic' env variables	1s
Build and check documentation	1m 38s
End-to-end tests, chromium	9m 56s
End-to-end tests, firefox	11m 57s
End-to-end tests, webkit	9m 56s
Run the Django test suite	7m 17s
Run the Django test suite in reverse	6m 24s
docker_build (extensions, token_exchange,prefill_haalcentraalhr, all-extensions-) / Build image	7m 2s
docker_build (production) / Build image	7m 3s
Check for unexepected OAS changes	4s
Validate OAS	13s
Generate Postman collection from OAS	10s
Generate SDKs from OAS	40s
Scan docker image	2m 9s
Push Docker image	0s
update-docker-readme	0s
	1h 4m 30s

Provide feedback