docs: def add_session(session=None):
      r"""Add a session to the SessionActivity table.
  
      :param session: Flask Session object to add. If None, ``session``
          is used. The object is expected to have a dictionary entry named
          ``"user_id"`` and a field ``sid_s``
      """
      user_id, sid_s = session['user_id'], session.sid_s
      with db.session.begin_nested():
          session_activity = SessionActivity(
              user_id=user_id,
              sid_s=sid_s,
              ip=request.remote_addr,
              country=_ip2country(request.remote_addr),
              **_extract_info_from_useragent(
                  request.headers.get('User-Agent', '')
              )
          )
          db.session.merge(session_activity)