我正在尝试在我的项目中使用hot-react-loader . 所以我更改了一些文件以使用它，但是当我编辑组件时出现错误 .

警告：React.createElement：type不应为null，undefined，boolean或number . 它应该是一个字符串（对于DOM元素）或一个ReactClass（对于复合组件） . [HMR]无法应用更新 . 需要做一个完整的重装！

我究竟做错了什么？

webpack.config.dev.js

var webpack               = require('webpack');
var path                  = require('path');
// Questo il plugin di webpack che mi genera  il file index.html in dist
var HtmlwebpackPlugin     = require('html-webpack-plugin');


const PATHS = {
    app: path.join(__dirname, 'app/index'),
    build: path.join(__dirname, 'dist')
};

module.exports = {
  devtool: 'eval',
    entry: [
    'webpack-dev-server/client?http://localhost:3500',
    'webpack/hot/only-dev-server',
    'react-hot-loader/patch',
    PATHS.app
  ],
    output: {
        path: PATHS.build,
        filename: 'js/bundle.js'
    },
    // Questo serve a non specificare le estensioni
    resolve: {
        extensions: ['', '.js']
    },
    module: {
        loaders: [
            {
                test: /\.js$/,
                loader: 'babel',
                exclude: /node_modules/
            },
            { test: /\.(png|jpg)$/, loader: "file?limit=1000&name=images/[hash].[ext]" },
            { test: /\.scss$/, loaders: [ 'style','css?modules&importLoaders=1&localIdentName=[path]___[name]__[local]___[hash:base64:5]' ] }
        ]
    },
    // Porta utilizzata da webpack-dev-server
    devServer: {
        port: 3500
    },
    plugins: [
    new webpack.HotModuleReplacementPlugin(),
        new HtmlwebpackPlugin({
            title: 'React Starter Kit',
            hash: true,
            inject: false,
            appMountId: 'app',
            template: 'jade!./app/assets/index.jade'
        })
    ]
};

server.js

var webpack = require('webpack');
var WebpackDevServer = require('webpack-dev-server');
var config = require('./webpack.config.dev');

new WebpackDevServer(webpack(config), {
  hot: true,
  historyApiFallback: true,
  stats: {
    colors: true
  }
}).listen(3500, 'localhost', function (err) {
  if (err) {
    console.log(err);
  }
  console.log('Listening at localhost:3500');
});

index.js

import ReactDOM from 'react-dom';
import React from 'react';
import App from './app';
import { AppContainer } from 'react-hot-loader';

const root = document.getElementById('app');

ReactDOM.render(
  <AppContainer>
    <App />
  </AppContainer>
  , root);

if (module.hot) {
  module.hot.accept('./app', () => {
    const App = require('./app');

    ReactDOM.render(
      <AppContainer>
        <App />
      </AppContainer>
    , root);
  });
}

app.js

import React from 'react';
import { Router, browserHistory } from 'react-router';
import routes from './routes/routes';

const App = () => (
    <Router history={browserHistory} routes={routes} />
);

export default App;