收到TypeError：无法读取未定义的属性“ map”

Question

我正在使用Material-UI进行一切正常的反应，但出现错误 TypeError：无法读取未定义的属性“ map” 。我还使用axio API来获取演示数据。我正在使用material-UI进行一切正常工作，但出现错误 TypeError：无法读取未定义的属性'map'。我也在使用axio API来获取演示数据。

import React, { Component } from 'react'
import ApiService from "../../service/ApiService";
import Table from '@material-ui/core/Table';
import TableBody from '@material-ui/core/TableBody';
import TableCell from '@material-ui/core/TableCell';
import TableHead from '@material-ui/core/TableHead';
import TableRow from '@material-ui/core/TableRow';
import Button from '@material-ui/core/Button';
import CreateIcon from '@material-ui/icons/Create';
import DeleteIcon from '@material-ui/icons/Delete';
import Typography from '@material-ui/core/Typography';

class ListUserComponent extends Component {

    constructor(props) {
        super(props)
        this.state = {
            users: [],
            message: null
        }
        this.deleteUser = this.deleteUser.bind(this);
        this.editUser = this.editUser.bind(this);
        this.addUser = this.addUser.bind(this);
        this.reloadUserList = this.reloadUserList.bind(this);
    }

    componentDidMount() {
        this.reloadUserList();
    }

    reloadUserList() {
        ApiService.fetchUsers()
            .then((res) => {
                this.setState({users: res.data.result})
            });
    }

    deleteUser(userId) {
        ApiService.deleteUser(userId)
           .then(res => {
               this.setState({message : 'User deleted successfully.'});
               this.setState({users: this.state.users.filter(user => user.id !== userId)});
           })
    }

    editUser(id) {
        window.localStorage.setItem("userId", id);
        this.props.history.push('/edit-user');
    }

    addUser() {
        window.localStorage.removeItem("userId");
        this.props.history.push('/add-user');
    }

    render() {
        return (
            <div>
                <Typography variant="h4" style={style}>User Details</Typography>
                <Button variant="contained" color="primary" onClick={() => this.addUser()}>
                    Add User
                </Button>

                <Table>
                    <TableHead>
                        <TableRow>
                            <TableCell>Id</TableCell>
                            <TableCell>FirstName</TableCell>
                            <TableCell align="right">LastName</TableCell>
                            <TableCell align="right">UserName</TableCell>
                            <TableCell align="right">Age</TableCell>
                            <TableCell align="right">Salary</TableCell>
                        </TableRow>
                    </TableHead>
                    <TableBody>
                        {this.state.users.map(row => (
                            <TableRow key={row.id}>
                                <TableCell component="th" scope="row">
                                    {row.id}
                                </TableCell>
                                <TableCell align="right">{row.firstName}</TableCell>
                                <TableCell align="right">{row.lastName}</TableCell>
                                <TableCell align="right">{row.username}</TableCell>
                                <TableCell align="right">{row.age}</TableCell>
                                <TableCell align="right">{row.salary}</TableCell>
                                <TableCell align="right" onClick={() => this.editUser(row.id)}><CreateIcon /></TableCell>
                                <TableCell align="right" onClick={() => this.deleteUser(row.id)}><DeleteIcon /></TableCell>

                            </TableRow>
                        ))}
                    </TableBody>
                </Table>

            </div>
        );
    }

}

const style ={
    display: 'flex',
    justifyContent: 'center'
}

export default ListUserComponent;