我尝试从对象输出数据，但出现错误“TypeError: 无法读取未定义的属性‘dropdownList’”，在 Lesson 数组之前所有对象都成功到达，但随后出现未定义，这可能是什么问题？其他所有 jsx 都已删除以提高可读性 https://ibb.co/hRytjMB https://ibb.co/6F1YcBr

Lesson.jsx

{
    this.props.lesson.dropdown.dropdownList.map(option =>
        items.push(<option>{option.par}</option>)
    )
}

lesson-reducer.js

import React from 'react';
import {faDotCircle} from "@fortawesome/free-solid-svg-icons/faDotCircle";

const ADD_LESSON = "ADD_LESSON";
const one = "Robby";

let initialState = {
    lessonsTitle: [
        {
            iconName: faDotCircle,
            description: [
                <span className="yourClass">{one}</span>,
                ` advanced diverted domestic sex repeated bringing you old.`
            ],
            dropdown: {
                titleName: "JSON",
                dropdownList: {
                    par: 'Hello World',
                }
            }

        },
        {
            titleName: "Boolean",
            iconName: faDotCircle,
            description: `
                Folly words widow one downs few age every seven. tolerably.
            `,
            languages: [
                'Язык HTML2',
            ]
        },
        {
            titleName: "Math",
            iconName: faDotCircle,
            description: `
               Another journey chamber way yet females man.
            `,
            languages: [
                'Язык HTML3',
            ]
        },
    ],

};