Do not str()ify None values, use self.repo.url instead.
Do not str()ify None values, use self.repo.url instead.

R=vadimsh@chromium.org
BUG=370554

Review URL: https://codereview.chromium.org/488813002

nicko96/Chrome-Infra,nicko96/Chrome-Infra,nicko96/Chrome-Infra,nicko96/Chrome-Infra,nicko96/Chrome-Infra