ember-component-css: Broken with latest ember-cli (2.4.0)

After upgrading to ember-cli and ember 2.4.0 I started getting this error, preventing the build to run:

this.vendorStaticStyles.concat is not a function
TypeError: this.vendorStaticStyles.concat is not a function
    at EmberApp.styles (/home/pablo/projects/kube-admin/node_modules/ember-component-css/index.js:85:43)
    at EmberApp.toArray (/home/pablo/projects/kube-admin/node_modules/ember-cli/lib/broccoli/ember-app.js:1493:10)
    at EmberApp.toTree (/home/pablo/projects/kube-admin/node_modules/ember-cli/lib/broccoli/ember-app.js:1514:30)
    at module.exports (/home/pablo/projects/kube-admin/ember-cli-build.js:25:14)
    at Class.module.exports.Task.extend.setupBroccoliBuilder (/home/pablo/projects/kube-admin/node_modules/ember-cli/lib/models/builder.js:55:19)
    at Class.module.exports.Task.extend.init (/home/pablo/projects/kube-admin/node_modules/ember-cli/lib/models/builder.js:89:10)
    at new Class (/home/pablo/projects/kube-admin/node_modules/ember-cli/node_modules/core-object/core-object.js:18:12)
    at Class.module.exports.Task.extend.run (/home/pablo/projects/kube-admin/node_modules/ember-cli/lib/tasks/serve.js:15:19)
    at /home/pablo/projects/kube-admin/node_modules/ember-cli/lib/commands/serve.js:70:22
    at lib$rsvp$$internal$$tryCatch (/home/pablo/projects/kube-admin/node_modules/rsvp/dist/rsvp.js:493:16)

If I change line 82 at index.js to this

inputFiles: this.vendorStaticStyles['/assets/vendor.css'].concat(['vendor/addons.css']),

then is working again. I’m preparing a PR for this

Apparently the structure of this.vendorStaticStyles changed. Is this private API?