React+Expressで掲示板を作成しています。

本の通りコードを書いていましたが、 node bbs-server.jsでlocalhostを立ち上げてみても、render()の中身が表示されません。
エラーにはTypeError: Cannot read property 'map' of undefinedと出てきます。
index.jsの

render(){
        const itemsHtml = this.state.items.map(e => (
            <li key={e._id}>{e.name} - {e.body}</li>
        ))

に原因があると思いますが、どこをどう直せば良いか分かりません。ご回答宜しくお願い致します。

---

使用しているツール
Node.js
Express
React
NeDB/SuperAgent

---

作成したプロジェクトのソースコードです。

package.json

{
  "name": "bbs",
  "version": "1.0.0",
  "description": "",
  "private": true,
  "main": "bundle.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "build": "webpack"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "express": "^4.17.1",
    "nedb": "^1.8.0",
    "superagent": "^5.1.0"
  },
  "devDependencies": {
    "@babel/core": "^7.5.5",
    "@babel/preset-env": "^7.5.5",
    "@babel/preset-react": "^7.0.0",
    "babel-loader": "^8.0.6",
    "react": "^16.8.6",
    "react-dom": "^16.8.6",
    "webpack": "^4.38.0",
    "webpack-cli": "^3.3.6"
  }
}

webpack.config.js

const path = require('path');
module.exports = {
    mode: 'production',
    entry: path.join(__dirname,'src/index.js'),
    output: {
        path: path.join(__dirname,'public'),
        filename: 'bundle.js'
    },
    devtool: 'inline-source-map',
    module: {
        rules: [{
            test: /\.(js|jsx)$/,
            use: [
                {
                    loader: "babel-loader",
                    options: {
                        presets: ["@babel/preset-env","@babel/react"]
                    }
                }
            ]
        }]
    }
};

index.js

import React from 'react';
import ReactDOM from 'react-dom';
import request from 'superagent';

class BBSForm extends React.Component{
    constructor(props){
        super(props)
        this.state = {
            name: '',
            body: ''
        }
    }

    nameChanged(e){
        this.setState({name: e.target.value})
    }
    bodyChanged(e){
        this.setState({body: e.target.value})
    }
    //write post
    post(e){
        request
        .get('/api/write')
        .query({
            name: this.state.name,
            body: this.state.body
        })
        .end((err,data) => {
            if(err){
                console.error(err)
            }
            this.setState({body: ''})
            if(this.props.onPost){
                this.props.onPost()
            }
        })
    }
    render(){
        return(
            <div>
                <label>名前: <br /></label>
                <input type='text' value={this.state.name} onChange={e => this.nameChanged(e)} />
                <br />
                <label>本文: <br /></label>
                <input type='text' value={this.state.body} size='60' onChange={e => this.bodyChanged(e)} />
                <br />
                <button onClick={e => this.post()}>発言する</button>
            </div>
        )
    }
}

class BBSApp extends React.Component{
    constructor(props){
        super(props)
        this.state = {
            items: []
        }
    }
    componentWillMount(){
        this.loadLogs()
    }
    loadLogs(){
        request
            .get('/api/getItems')
            .end((err,data) => {
                if(err){
                    console.error(err)
                    return
                }
                this.setState({items: data.body.logs})
            })
        }
    render(){
        const itemsHtml = this.state.items.map(e => (
            <li key={e._id}>{e.name} - {e.body}</li>
        ))
        return(
            <div>
                <h1>掲示板</h1>
                <BBSForm onPost={e => this.loadLogs()} />
                <p><button onClick={e => this.loadLogs()}>再読み込み</button></p>
                <ul>{itemsHtml}</ul>
            </div>
        )
    }
}
ReactDOM.render(
    <BBSApp />,
    document.getElementById('root')
)

bbs-server.js

//bbs web server
const NeDB = require('nedb');
const path = require('path');
const db = new NeDB({
    filename: path.join(__dirname,'bbs.db'),
    autoload: true
});
const doc = {
    name: "author",
    body: "test"
}
db.insert(doc,function(err,newdoc){
    console.log(newdoc._id)
})

db.loadDatabase();

//open server
const express = require('express');
const app = express();
const portNo = 3001;
app.listen(portNo,() => {
    console.log('Open Server', `http://localhost:${portNo}`);
})

app.use('/public', express.static('./public'))
app.get('/', (req,res) => {
    res.redirect(302,'/public')
})

//API
app.get('/api/getItems', (req,res) => {
    db.find({}).sort({stime: 1}).exec((err,data) => {
        if(err){
            sendJSON(res,false,{logs: [],msg: err})
            return
        }
        console.log(data)
        sendJSON(res,true,{logs: data})
    })
})

//new LOG
app.get('/api/write', (req,res) => {
    const q = req.query
    db.insert({
        name: q.name,
        body: q.body,
        stime: (new Date()).getTime()

    },(err,doc) => {
        if(err) {
            console.error(err)
            sendJSON(res,false,{msg: err})
            return
        }
        sendJSON(res,true,{id: doc._id})
    })
})

function sendJSON(res,result,obj){
    obj['result'] = result
    res.json('obj')
}

質問は以上です。ご回答宜しくお願い致します。