docs: def _http_req_apply_default_headers(self, request_headers,
                                          content_type, body):
          """Set default values for common HTTP request headers
  
          :param dict request_headers: The HTTP request headers
          :param content_type: The mime-type used in the request/response
          :type content_type: :py:class:`ietfparse.datastructures.ContentType`
              or str
          :param mixed body: The request body
          :rtype: dict
  
          """
          if not request_headers:
              request_headers = {}
          request_headers.setdefault(
              'Accept', ', '.join([str(ct) for ct in AVAILABLE_CONTENT_TYPES]))
          if body:
              request_headers.setdefault(
                  'Content-Type', str(content_type) or str(CONTENT_TYPE_MSGPACK))
          if hasattr(self, 'correlation_id'):
              request_headers.setdefault(
                  'Correlation-Id', self.correlation_id)
          elif hasattr(self, 'request') and \
                  self.request.headers.get('Correlation-Id'):
              request_headers.setdefault(
                  'Correlation-Id', self.request.headers['Correlation-Id'])
          return request_headers