Sass加载器在Webpack中不起作用

我正在尝试在Webpack配置中支持* .scss文件，但是在运行webpack build命令时，始终出现以下错误：

ERROR in ./~/css-loader!./~/sass-loader!./app/styles.scss
Module build failed: TypeError: Cannot read property 'sections' of null
at new SourceMapConsumer (/Users/sean/Development/playground/webpack.sass.test/node_modules/css-loader/node_modules/postcss/node_modules/source-map/lib/source-map/source-map-consumer.js:23:21)
at PreviousMap.consumer (/Users/sean/Development/playground/webpack.sass.test/node_modules/css-loader/node_modules/postcss/lib/previous-map.js:37:34)
at new Input (/Users/sean/Development/playground/webpack.sass.test/node_modules/css-loader/node_modules/postcss/lib/input.js:42:28)
at parse (/Users/sean/Development/playground/webpack.sass.test/node_modules/css-loader/node_modules/postcss/lib/parse.js:17:17)
at new LazyResult (/Users/sean/Development/playground/webpack.sass.test/node_modules/css-loader/node_modules/postcss/lib/lazy-result.js:54:47)
at Processor.process (/Users/sean/Development/playground/webpack.sass.test/node_modules/css-loader/node_modules/postcss/lib/processor.js:30:16)
at processCss (/Users/sean/Development/playground/webpack.sass.test/node_modules/css-loader/lib/processCss.js:168:24)
at Object.module.exports (/Users/sean/Development/playground/webpack.sass.test/node_modules/css-loader/lib/loader.js:21:15)
@ ./app/styles.scss 4:14-117

我无法为自己的生活弄清楚原因。这是一个非常基本的设置。

我创建了一个保管箱共享，其中最少的说明了这一点：https : //www.dropbox.com/s/quobq29ngr38mhx/webpack.sass.test.zip?dl=0

解压缩然后运行：

npm install
webpack

这是我的webpack.config.js文件：

var path = require('path')
var webpack = require('webpack')

module.exports = {
  devtool: 'eval',
  entry: [
    './app'
  ],
  output: {
    path: path.join(__dirname, 'dist'),
    filename: 'index.js',
    publicPath: '/dist/'
  },
  plugins: [
    new webpack.NoErrorsPlugin()
  ],
  resolve: {
    extensions: ['', '.js']
  },
  module: {
    loaders: [{
      test: /\.scss$/,
      loader: 'style-loader!css-loader!sass-loader'
    }]
  }
}

还有index.js入口文件：

require('./styles.scss');

alert('foo bar baz');

以及styles.scss文件：

body {
  background-color: #000;
}

它似乎遵循sass-loader文档站点的建议，但我无法使其运行。

有关我的环境的信息：

node - 0.12.4
npm  - 2.10.1
os   - OS X Yosemite