Attempts to Fork a repo to existing location gives vauge error message

Problem to solve

If you've a user who is attempting to fork a repository, they may unknowingly choose a location where the repository has been forked to in the past. The error message in this event is: An error occurred while forking the project. Please try again.

Proposal

Generate an error message to the user that says precisely what happened. Perhaps language on how to avoid it, or a link to the existing location. Anything to give us a clue would be greatly appreciated.

Intended users

Any users who attempts a fork.