Doctor: Unable to get merge base for closed PR with deleted branch

Hi,

I am looking into upgrading my gitea instance (running in docker, backed by postgres).

To ensure everything goes smoothly, I ran docker-compose exec --user git gitea gitea doctor --all.
This gives me a number of warnings for closed Pull Requests where the branch has been deleted.
These warnings take the form of

[W] Unable to get merge base for PR ID <pr_id>, #<pr_number> onto <branch> in <repo>. Error exit status 128 - fatal: Not a valid object name <branch>
  - fatal: Not a valid object name <branch>
  & exit status 128 - fatal: ambiguous argument 'refs/heads/<branch>': unknown revision or path not in the working tree.
  Use '--' to separate paths from revisions, like this:
  'git <command> [<revision>...] -- [<file>...]'
  - fatal: ambiguous argument 'refs/heads/<branch>': unknown revision or path not in the working tree.
  Use '--' to separate paths from revisions, like this:
  'git <command> [<revision>...] -- [<file>...]'

It’s still possible to view the pull requests on the site, but obviously the source and target branch links are broken.
It also shows " This pull request cannot be reopened because the branch was deleted. " as expected.

It’s very easy to lose track of actual issues because of all these reports.
Is there a way to make gitea doctor accept these kinds of pull request?