鼠标悬停在一级menu菜单时，二级菜单不显示，报如下错误：
react：16.13
antd：4.6.5

class NavLeft extends Component {
    render() {
        return (
            <div>
                <div className="logo">
                    <img src="/assets/logo-ant.svg" />
                    <h1>April MS</h1>
                </div>
                <Menu>
                    <SubMenu key="sub1" title="Navigation Two">
                        <Menu.Item key="1">Option 3</Menu.Item>
                        <Menu.Item key="2">Option 4</Menu.Item>
                        <Menu.Item key="3">Option 5</Menu.Item>
                        <Menu.Item key="4">Option 6</Menu.Item>
                    </SubMenu>
                </Menu>
            </div>
        )
    }
}