Editing Branch Permission on a repo is broken if the particular branch permission contains a user who does not have any permissions to the repo anymore

Steps to Reproduce:

1. Add a user as a group member in a team account – make sure the user has at least write access to repos
2. Add a branch permission to a repo, and add the user into the branch permission
3. Remove the user from the team

Expected Result:

It should still be possible to edit the branch permission.

Actual Result

Trying to edit the branch permission will end up with an error message 'Unexpected error has occured'

Workaround
Re-add the affected Branch Permission