def create_milestone(self, title, state=github.GithubObject.NotSet, description=github.GithubObject.NotSet, due_on=github.GithubObject.NotSet):
        """
        :calls: `POST /repos/:owner/:repo/milestones <http://developer.github.com/v3/issues/milestones>`_
        :param title: string
        :param state: string
        :param description: string
        :param due_on: datetime
        :rtype: :class:`github.Milestone.Milestone`
        """
        assert isinstance(title, (str, unicode)), title
        assert state is github.GithubObject.NotSet or isinstance(state, (str, unicode)), state
        assert description is github.GithubObject.NotSet or isinstance(description, (str, unicode)), description
        assert due_on is github.GithubObject.NotSet or isinstance(due_on, (datetime.datetime, datetime.date)), due_on
        post_parameters = {
            "title": title,
        }
        if state is not github.GithubObject.NotSet:
            post_parameters["state"] = state
        if description is not github.GithubObject.NotSet:
            post_parameters["description"] = description
        if due_on is not github.GithubObject.NotSet:
            if isinstance(due_on, datetime.date):
                post_parameters["due_on"] = due_on.strftime("%Y-%m-%dT%H:%M:%SZ")
            else:
                post_parameters["due_on"] = due_on.isoformat()
        headers, data = self._requester.requestJsonAndCheck(
            "POST",
            self.url + "/milestones",
            input=post_parameters
        )
        return github.Milestone.Milestone(self._requester, headers, data, completed=True)