Argh what am i doing wrong?

Sorry, this is likely a dumb question but all I'm trying to do here is simply telnet into a device. My console.log at the end is continually returning undefined and the debug.txt never has anything in it. I've also noticed that when i use .on instead of .when (for the expect statements) i actually get some kind of output although it's an error. Using .when gives me nothing. Im using suppose version 0.6.2. Any idea where I'm being dumb here?

const suppose = require('suppose');
const fs = require('fs')

suppose('telnet' ['10.0.0.91'],{ debug: fs.createWriteStream('/tmp/debug.txt') })
.when('login:').respond('admin\n')
.when('Password:').respond('password')
 .on('error', function(err){
    console.log(err.message);
 })
    .end(function(code) {
        console.log(code);
    });

Start by reproducing the suppose 0.6.2 telnet example with the shown .when/.respond chain, the .on error handler, and the debug stream. Compare the .when and .on behavior; done means the session reaches the prompts, writes debug.txt, and reports a completion code or a clear error.