How to solve "callback not fired" with Vows and Node.js

I'm trying to get started with Vows and Vows-BDD. Unfortunately, the callbacks are tripping me up.

In the very simple example below, how does one fix this error?

** Inside the first context
** Creating Person with name Nick

✗ Errored » callback not fired
      in Create a Person via JavaScript: When a person has a name,
      in Creating a Person
      in undefined✗ Errored » 1 errored  1 dropped

vows_bdd  = require "vows-bdd"
assert    = require "assert"


class Person
  constructor: (@name) ->
    console.log "** Creating Person with name #{@name}"

  greeting: ->
    "Hello, #{@name}"


vows_bdd
  .Feature("Creating a Person")
    .scenario("Create a Person via JavaScript")

    .when "a person has a name", ->
      console.log "** Inside the first context"
      new Person "Nick"

    .then "the person can be greeted", (person) ->
      console.log "person is a #{typeof person} = [#{person}]"
      assert.equal person.greeting(), "Hello, Nick"

    .complete()
    .finish(module)