async def connection_exists(ssid: str) -> Optional[str]:
    """ If there is already a connection for this ssid, return the name of
    the connection; if there is not, return None.
    """
    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
If there is already a connection for this ssid, return the name of
    the connection; if there is not, return None.