Javascript 反应错误'；TypeError:无法将未定义或null转换为对象'；

我不知道为什么我会在控制台中出现这个错误

TypeError: Cannot convert undefined or null to object
    at ContestList (/Users/antonio-pavicevac-ortiz/Dropbox/developer_folder/my-fullstack-javascript-app/src/components/ContestList.jsx:8:15)
    at /Users/antonio-pavicevac-ortiz/Dropbox/developer_folder/my-fullstack-javascript-app/node_modules/react-dom/lib/ReactCompositeComponent.js:305:16
    at measureLifeCyclePerf (/Users/antonio-pavicevac-ortiz/Dropbox/developer_folder/my-fullstack-javascript-app/node_modules/react-dom/lib/ReactCompositeComponent.js:75:12)
    at ReactCompositeComponentWrapper._constructComponentWithoutOwner (/Users/antonio-pavicevac-ortiz/Dropbox/developer_folder/my-fullstack-javascript-app/node_modules/react-dom/lib/ReactCompositeComponent.js:304:14)
    at ReactCompositeComponentWrapper._constructComponent (/Users/antonio-pavicevac-ortiz/Dropbox/developer_folder/my-fullstack-javascript-app/node_modules/react-dom/lib/ReactCompositeComponent.js:279:21)
    at ReactCompositeComponentWrapper.mountComponent (/Users/antonio-pavicevac-ortiz/Dropbox/developer_folder/my-fullstack-javascript-app/node_modules/react-dom/lib/ReactCompositeComponent.js:187:21)
    at Object.mountComponent (/Users/antonio-pavicevac-ortiz/Dropbox/developer_folder/my-fullstack-javascript-app/node_modules/react-dom/lib/ReactReconciler.js:45:35)
    at ReactDOMComponent.mountChildren (/Users/antonio-pavicevac-ortiz/Dropbox/developer_folder/my-fullstack-javascript-app/node_modules/react-dom/lib/ReactMultiChild.js:236:44)
    at ReactDOMComponent._createContentMarkup (/Users/antonio-pavicevac-ortiz/Dropbox/developer_folder/my-fullstack-javascript-app/node_modules/react-dom/lib/ReactDOMComponent.js:659:32)
    at ReactDOMComponent.mountComponent (/Users/antonio-pavicevac-ortiz/Dropbox/developer_folder/my-fullstack-javascript-app/node_modules/react-dom/lib/ReactDOMComponent.js:526:29)
TypeError: Cannot read property 'initialMarkup' of undefined
    at /Users/antonio-pavicevac-ortiz/Dropbox/developer_folder/my-fullstack-javascript-app/routes/index.js:12:47
    at process._tickDomainCallback (internal/process/next_tick.js:135:7)

这是有问题的文件：

import React from 'react';
import ContestPreview from './ContestPreview';
import PropTypes from 'prop-types';

export default function ContestList({ contests, onContestClick }) {
  return (
    <div className="ContestList">
      {Object.keys(contests).map(contestId => (
        <ContestPreview
          key={contestId}
          onClick={onContestClick}
          {...contests[contestId]}
        />
      ))}
    </div>
  );
}

ContestList.propTypes = {
  contests: React.PropTypes.object,
  onContestClick: React.PropTypes.func.isRequired
};

api/contracts.js：

'use strict';

var express = require('express');
var data = require('../../src/testData');
const router = express.Router();

const contests = data.contests.reduce(function(obj, contest) {
  obj[contest.id] = contest;
  return obj;
}, {});

router.get('/', function(req, res) {
  res.send({
    contests: contests
  });
});

router.get('/:contestId', function(req, res) {
  let contest = contests[req.params.contestId];
  contest.description =
    'Food truck gluten-free banksy, fap occupy bespoke whatever mustache.  Occupy kogi kale chips chillwave, odd future typewriter iphone twee truffaut viral ethical artisan put a bird on it single-origin coffee banh mi.  Master cleanse brunch occupy trust fund marfa yr.  Chillwave ennui fap, wes anderson cliche cosby sweater brooklyn vegan organic.  Shoreditch PBR semiotics, chillwave art party photo booth terry richardson.  Synth ennui semiotics mustache pickled, biodiesel food truck cosby sweater readymade mixtape letterpress pour-over leggings.  Food truck freegan vinyl thundercats, post-ironic ennui wes anderson banh mi four loko synth photo booth authentic 3 wolf moon.';
  res.send(contest);
});

module.exports = router;

---

尝试向ConentList添加默认道具，如下所示

contesticsList.defaultProps={contestics:{}，}使用这个
{Object.keys（竞赛{124;{}）
现在，当您获得数据时，它将呈现组件，并且它将提供默认值作为
{}
尝试向ConentList添加默认的道具，就像这样
竞赛列表。默认道具={竞赛：{}，}；
使用这个
{Object key.keys（竞赛}）
现在，当您获取数据时，它将呈现组件，并提供默认值
{}
//fetch the data from the api
import React from 'react';
import ReactDomServer from 'react-dom/server';

import App from './src/components/App';

var axios = require('axios');
import config from './config';

const getApiUrl = contestId => {
  if (contestId) {
    return `http://localhost:8016/api/contests/${contestId}`;
  }
  return `http://localhost:8016/api/contests`;
};

const getInitialData = (contestId, apiData) => {
  if (contestId) {
    return {
      currentContestId: apiData.id,
      contests: {
        [apiData.id]: apiData
      }
    };
  }
  return {
    contests: apiData.contests
  };
};

const serverRender = contestId =>
  axios
    .get(getApiUrl(contestId))
    .then(resp => {
      const initialData = getInitialData(contestId, resp.data);
      return {
        initialMarkup: ReactDomServer.renderToString(
          <App initialData={resp.data} />
        ),
        initialData: resp.data
      };
    })
    .catch(console.error);

export default serverRender;

'use strict';

var express = require('express');

const router = express.Router();

import serverRender from '../serverRender';

router.get(['/', '/contest/:contestId'], function(req, res) {
  console.log(req.params.contestId);
  serverRender(req.params.contestId)
    .then(({ initialMarkup, initialData }) => {
      res.render('index', {
        initialMarkup,
        initialData
      });
    })
    .catch(console.error);
});

module.exports = router;

'use strict';

var express = require('express');
var data = require('../../src/testData');
const router = express.Router();

const contests = data.contests.reduce(function(obj, contest) {
  obj[contest.id] = contest;
  return obj;
}, {});

router.get('/', function(req, res) {
  res.send({
    contests: contests
  });
});

router.get('/:contestId', function(req, res) {
  let contest = contests[req.params.contestId];
  contest.description =
    'Food truck gluten-free banksy, fap occupy bespoke whatever mustache.  Occupy kogi kale chips chillwave, odd future typewriter iphone twee truffaut viral ethical artisan put a bird on it single-origin coffee banh mi.  Master cleanse brunch occupy trust fund marfa yr.  Chillwave ennui fap, wes anderson cliche cosby sweater brooklyn vegan organic.  Shoreditch PBR semiotics, chillwave art party photo booth terry richardson.  Synth ennui semiotics mustache pickled, biodiesel food truck cosby sweater readymade mixtape letterpress pour-over leggings.  Food truck freegan vinyl thundercats, post-ironic ennui wes anderson banh mi four loko synth photo booth authentic 3 wolf moon.';
  res.send(contest);
});

module.exports = router;