What password is sent when a router does not have a password set?
The program does not currently support networks without passwords.
You can amend the program to fix that by editing the source code file /bssid/connect-ssid.swift. You'll want to remove lines 42 and 43:
print("Input WiFi password")
let password = String(cString: getpass(""))
And replace them with:
let password: String? = nil