code: def create_milestone(self, title, state=None, description=None,
                           due_on=None):
          
          url = self._build_url('milestones', base_url=self._api)
          if state not in ('open', 'closed'):
              state = None
          data = {'title': title, 'state': state,
                  'description': description, 'due_on': due_on}
          self._remove_none(data)
          json = None
          if data:
              json = self._json(self._post(url, data=data), 201)
          return Milestone(json, self) if json else None
docs: Create a milestone for this repository.
  
          :param str title: (required), title of the milestone
          :param str state: (optional), state of the milestone, accepted
              values: ('open', 'closed'), default: 'open'
          :param str description: (optional), description of the milestone
          :param str due_on: (optional), ISO 8601 formatted due date
          :returns: :class:`Milestone <github3.issues.milestone.Milestone>` if
              successful, otherwise None