code: def merge(self, base, head, message=''):
          
          url = self._build_url('merges', base_url=self._api)
          data = {'base': base, 'head': head}
          if message:
              data['commit_message'] = message
          json = self._json(self._post(url, data=data), 201)
          return RepoCommit(json, self) if json else None
docs: Perform a merge from ``head`` into ``base``.
  
          :param str base: (required), where you're merging into
          :param str head: (required), where you're merging from
          :param str message: (optional), message to be used for the commit
          :returns: :class:`RepoCommit <github3.repos.commit.RepoCommit>`