Fetch the repo. If the local copy was updated, return True. If the
        local copy was already up-to-date, return False.

def _fetch(self):
        '''
        Fetch the repo. If the local copy was updated, return True. If the
        local copy was already up-to-date, return False.
        '''
        origin = self.repo.remotes[0]
        try:
            fetch_results = origin.fetch()
        except AssertionError:
            fetch_results = origin.fetch()

        new_objs = False
        for fetchinfo in fetch_results:
            if fetchinfo.old_commit is not None:
                log.debug(
                    '%s has updated \'%s\' for remote \'%s\' '
                    'from %s to %s',
                    self.role,
                    fetchinfo.name,
                    self.id,
                    fetchinfo.old_commit.hexsha[:7],
                    fetchinfo.commit.hexsha[:7]
                )
                new_objs = True
            elif fetchinfo.flags in (fetchinfo.NEW_TAG,
                                     fetchinfo.NEW_HEAD):
                log.debug(
                    '%s has fetched new %s \'%s\' for remote \'%s\'',
                    self.role,
                    'tag' if fetchinfo.flags == fetchinfo.NEW_TAG else 'head',
                    fetchinfo.name,
                    self.id
                )
                new_objs = True

        cleaned = self.clean_stale_refs()
        return True if (new_objs or cleaned) else None