code: async def connection_exists(ssid: str) -> Optional[str]:
      
      nmcli_conns = await connections()
      for wifi in [c['name']
                   for c in nmcli_conns if c['type'] == 'wireless']:
          res, _ = await _call(['-t', '-f', '802-11-wireless.ssid',
                                '-m', 'tabular',
                                'connection', 'show', wifi])
          if res == ssid:
              return wifi
      return None
docs: If there is already a connection for this ssid, return the name of
      the connection; if there is not, return None.