Normalize the hooks_uuid field before saving the repository.
Review Request #6362 — Created Sept. 23, 2014 and submitted
The hooks_uuid field would become a blank string after editing in the
admin UI. This resulted in a collision as soon as there was more than
one entry with a blank string.We now normalize this to None if blank prior to saving.
Saved a repository that had a blank string saved from a prior edit. Checked
in the database, and saw that it turned into a NULL.