Transfer a repository will result in pull requests from the same repository broken #8563
Description
There is a duplicated column named HeadUserName on PullRequest. But if HeadRepo transfered to a new place, we haven't change the pull requests' HeadUserName.
There are two method to resolve the problem. One is update all PullRequest's HeadUserName when transfered repository.
The second is to remove the column HeadUserName and get it from Repository and User.
Which one is better?
