given the title as str, looks for an existing milestone or create a new one,
        and return the object

def get_milestone(self, title):
        """
        given the title as str, looks for an existing milestone or create a new one,
        and return the object
        """
        if not title:
            return GithubObject.NotSet
        if not hasattr(self, '_milestones'):
            self._milestones = {m.title: m for m in self.repo.get_milestones()}

        milestone = self._milestones.get(title)
        if not milestone:
            milestone = self.repo.create_milestone(title=title)
        return milestone