title: Ember build failed because of broccoliBuilderError
body: <p>I am on an ember project and I am trying to upgrade ember version from 2.8 to 3.5.0. But since I changed the version and also some several dependencies version I get this error :</p>
  
  <p><a href="https://i.stack.imgur.com/mqNYz.png" rel="nofollow noreferrer">Error stack</a></p>
  
  <p>I've tried to fix this with ember-cli-build file but the error persisted.</p>
  
  <pre><code>const EmberApp = require('ember-cli/lib/broccoli/ember-app');
  
  module.exports = function(defaults) {
      const isPublicEnv = EmberApp.env() === 'public';
  
      const app = new EmberApp(defaults, {
  
          'sassOptions': {
              includePaths: [
                  'bower_components/materialize/sass',
              ],
          },
          'outputPaths': {
              app: {
                  css: {
                      design1: '/assets/design1.css',
                      design2: '/assets/design2.css'
                  },
              },
          },
          'ember-cli-babel': {
              includePolyfill: true,
          },
          'minifyJS': {
              enabled: isPublicEnv,
          },
          'minifyCSS': {
              enabled: isPublicEnv,
          },
          'fingerprint': {
              enabled: isPublicEnv,
          },
          'tests': !isPublicEnv,
          'hinting': !isPublicEnv,
          'sourcemaps': {
              enabled: !isPublicEnv,
          },
      });
  
      app.import('vendor/lib1.js');
      app.import('vendor/lib2.js');
  
      return app.toTree();
  };
  </code></pre>
  
  <p>Any suggestion to resolve this ?</p>