TypeError: Cannot read property 'addReference' of undefined

[andrewhl]

(Originally posted this on gridsome, reposting here)

I'm using Gridsome ^0.3.0, and @gridsome/source-wordpress, ^0.1.0, and I'm running into the following error upon running gridsome develop:

TypeError: Cannot read property 'addReference' of undefined
    at WordPressSource.fetchWordPressContent (/Users/andrew/code/SpiralPraxis/marketing/node_modules/@gridsome/source-wordpress/index.js:99:20)
    at <anonymous>
    at process._tickCallback (internal/process/next_tick.js:188:7)

I've got a vanilla installation. I haven't modified any files except gridsome.config.js, and that only to provide a URL to my wordpress site, which is enabled to serve wp-json endpoints.

Here's my config file:

module.exports = {
  plugins: [{
    use: '@gridsome/source-wordpress',
    options: {
      baseUrl: 'https://mywordpresssite.com', // required
      typeName: 'WordPress', // GraphQL schema name (Optional)
      perPage: 100, // How many posts to load from server per request (Optional)
      concurrent: 10, // How many requests to run simultaneously (Optional)
      routes: {
        post: '/:year/:month/:day/:slug', //adds route for "post" post type (Optional)
        post_tag: '/tag/:slug' // adds route for "post_tag" post type (Optional)
      }
    }
  }]
}

Here's the relevant code from @gridsome/source-wordpress/index.js:

    for (const type in taxonomies) {
      const options = taxonomies[type]
      const typeName = makeTypeName(type)
      const route = routes[type] || `/${options.rest_base}/:slug`

      restBases.taxonomies[type] = options.rest_base

      for (const type of options.types) {
        const postTypeName = makeTypeName(type)
        const collection = getContentType(postTypeName)

        collection.addReference(options.rest_base, { typeName, key: '_id' })
      }

      addContentType({ typeName, route })
    }

Not sure what to do. I can't see anything in the documentation that clarifies this issue. Help would be appreciated.