title: webpack + babel loader source map references empty file
body: <p>I have an es6 project which I bundle using webpack + babel loader.
  When I open the devtools I can see 'webpack://' and all my sources (es6) underneath.</p>
  
  <p>The problems are: breakpoints don't hit and function references directs me to a file name '?d41d</p>
  
  <p>which has the following content:</p>
  
  <pre><code>undefined
  
  
  /** WEBPACK FOOTER **
   ** 
   **/
  </code></pre>
  
  <p>if I drill down from document script to a function in my bundle I get to the ?d41d file as well</p>
  
  <p>my webpack.config.js:</p>
  
  <pre><code>module.exports = {
  
      debug: true,
      devtool: 'cheap-module-eval-source-map',
      entry: "entry.js",
      output: {
          path: "C:/html5/",
          filename: "bundle.js"
      },
      module: {
          loaders: [
              {
                  test: /\.js$/,
                  exclude: /(node_modules|bower_components)/,
                  loader: 'babel',
                  query: {
                      presets: ['es2015'],
                      plugins: ['transform-object-assign'],
                      sourceMaps: ['inline']
                  }
              }
          ]
      }
  };
  </code></pre>
  
  <p>and part of package.json in case it might help:</p>
  
  <pre><code>"devDependencies": {
      "ava": "^0.16.0",
      "babel-core": "^6.14.0",
      "babel-loader": "^6.2.5",
      "babel-plugin-transform-object-assign": "^6.8.0",
      "babel-preset-es2015": "^6.13.2",
      "cheerio": "^0.22.0",
      "chokidar-cli": "^1.2.0",
      "eslint": "^3.3.1",
      "html-to-js": "0.0.1",
      "jsdoc": "^3.4.0",
      "jsdom": "^9.4.2",
      "minami": "^1.1.1",
      "obfuscator": "^0.5.4",
      "sinon": "^1.17.5",
      "uglify-js": "^2.7.3",
      "webpack": "^1.13.2",
      "yargs": "^5.0.0"
    },
    "dependencies": {
      "jquery": "^3.1.0"
    }
  </code></pre>
  
  <p>Thanks in advance.</p>