docs: def create_git_ref(self, ref, sha):
          """
          :calls: `POST /repos/:owner/:repo/git/refs <http://developer.github.com/v3/git/refs>`_
          :param ref: string
          :param sha: string
          :rtype: :class:`github.GitRef.GitRef`
          """
          assert isinstance(ref, (str, unicode)), ref
          assert isinstance(sha, (str, unicode)), sha
          post_parameters = {
              "ref": ref,
              "sha": sha,
          }
          headers, data = self._requester.requestJsonAndCheck(
              "POST",
              self.url + "/git/refs",
              input=post_parameters
          )
          return github.GitRef.GitRef(self._requester, headers, data, completed=True)