问错误:不变冲突: Grid.render()

EN

import {Grid} from 'react-bootstrap';
import {Row} from 'react-bootstrap';
import {Col} from 'react-bootstrap';

class Application extends React.Component {
render() {
    var Handler = this.props.currentRoute.get('handler');

    return (
        <div>
          <Grid>
            <Row>
                 <Col xs={12} md={8}>
                     <Nav selected={this.props.currentPageName} links={this.props.pages} />
                </Col>
            </Row>
            <Row>
                <Col>
                    <Handler />
                </Col>
            </Row>
          </Grid>
        </div>
    );
}