Create pull screen breaks if originator has no commits (BB-7276)

1. I forked a repo that hasn't yet had a commit.
2. cloned and pushed to my account.
3. Tried to create a pull request but I get an endless progress wheel and javascript error "cannot call method 'split' of null. The source is minified, but I think the issue is the right hand pane is trying to populate the branches of the parent repo but doesn't find anything due to lack of initial commit.

Not a big deal but a bit puzzling until I figured out the issue.