def edit(self, sha, force=github.GithubObject.NotSet):
        """
        :calls: `PATCH /repos/:owner/:repo/git/refs/:ref <http://developer.github.com/v3/git/refs>`_
        :param sha: string
        :param force: bool
        :rtype: None
        """
        assert isinstance(sha, (str, unicode)), sha
        assert force is github.GithubObject.NotSet or isinstance(force, bool), force
        post_parameters = {
            "sha": sha,
        }
        if force is not github.GithubObject.NotSet:
            post_parameters["force"] = force
        headers, data = self._requester.requestJsonAndCheck(
            "PATCH",
            self.url,
            input=post_parameters
        )
        self._useAttributes(data)