The Milestone that the Ticket is a part of

def milestone(self, extra_params=None):
        """
        The Milestone that the Ticket is a part of
        """
        if self.get('milestone_id', None):
            milestones = self.space.milestones(id=self['milestone_id'], extra_params=extra_params)
            if milestones:
                return milestones[0]