code: def merge(self, commit_message='', sha=None):
          
          parameters = {'commit_message': commit_message}
          if sha:
              parameters['sha'] = sha
          url = self._build_url('merge', base_url=self._api)
          json = self._json(self._put(url, data=dumps(parameters)), 200)
          self.merge_commit_sha = json['sha']
          return json['merged']
docs: Merge this pull request.
  
          :param str commit_message: (optional), message to be used for the
              merge commit
          :returns: bool