Ember.js CLI Build Broccoli Funnel not working

I am trying to use the Broccoli Funnel package to pull a complete directory into my assets folder in an Ember CLI build. Please find my ember-cli-build.js file below:

var EmberApp = require('ember-cli/lib/broccoli/ember-app');
var Funnel = require('broccoli-funnel');

module.exports = function(defaults) {
  var app = new EmberApp(defaults, {
    //
  });

  var extraAssets = new Funnel('vendor/images/frames/artist/64', {
    destDir: '/assets/images'
  });

  app.toTree(extraAssets);

  return app.toTree();
};

The directory "vendor/images/frames/artist/64" only contains .png image files and I would like to have them all available after the build at "assets/images/64/". After a build process, there is no images folder created in my assets directory.

Can you help advise where I have gone wrong? Are there any debugging tools to show what Broccoli Funnel is trying to add to the build and where those files are being distributed to?