in wifi-password/node_modules/linux-wifi-password/index.js, I needed to change line 7 from
var args = ['cat', '/etc/NetworkManager/system-connections ' + ssid];
to
var args = ['cat', '/etc/NetworkManager/system-connections/Auto\ ' + ssid];
(the difference being /Auto\)
I appreciate that this package has taught me where this info is located. I'm not sure which other systems this fix might be needed in as well.