MR list is empty when filtering by approver

Summary

When i search the global MR list by approver, there are 0 results and I see an "error" prompting me to add a filter to see results:

Steps to reproduce

Visit this link: https://gitlab.com/dashboard/merge_requests?scope=all&utf8=%E2%9C%93&state=opened&approver_usernames[]=joshfriend

What is the current bug behavior?

No MRs are shown

What is the expected correct behavior?

I should see all the MRs that list the selected user(s) as an approver

Relevant logs and/or screenshots

see above

Output of checks

This bug happens on GitLab.com