Merge request consistently throws 500 error code

Summary

Try to open the merge request inkscape/inkscape!9 (closed). I get 500 error responses all the time, so I can't edit (or delete) it.

Steps to reproduce

1. Navigate to inkscape/inkscape!9 (closed).
2. Notice the 500 error code page.
3. No, that's all.

What is the current bug behavior?

The merge request shows a 500 error code page.

What is the expected correct behavior?

I'd expected the details of the merge request.

Output of checks

This bug happens on GitLab.com.