控制台错误-未捕获的TypeError：无法读取未定义的属性'setState'-openModal（）

Question

链接到GitHub上的该项目： https://github.com/sheedSVNTH/MERN-expense-manager-app

我收到错误：未捕获的TypeError：无法读取未定义的属性'setState'

我已经正确绑定了“ this”。这是我的代码段。

import React from 'react';
import {Button} from 'react-bootstrap';
import Modal from 'react-modal';
import axios from 'axios';
import {Link} from 'react-router-dom';
var querystring = require('querystring');

class Add extends React.Component {
    constructor() {
        super();
        this.state = {
            description: '',
            amount: '',
            month: '',
            year: '',
            messageFromServer: '',
            modalIsOpen: false
        }

    this.handleSelectChange = this.handleSelectChange.bind(this);
    this.onClick = this.onClick.bind(this);
    this.handleTextChange = this.handleTextChange.bind(this);
    this.insertNewExpense = this.insertNewExpense.bind(this);
    this.openModel = this.openModal.bind(this);
    this.closeModal = this.closeModal.bind(this);
}
openModal() {
    this.setState({modalIsOpen: true});
}
closeModal() {
    this.setState({
        modalIsOpen: false,
        description: '',
        amount: '',
        month: 'Jan',
        year: 2018,
        messageFromServer: ''
    });
}