在react-native中，组件react-navigation不使用headerMode为none，就出现报错。

Question

react-navigation不使用headerMode为none，就出现报错

 import React, { Component } from 'react';
 import {
     Text,
     View,
     Button,
     StyleSheet
 } from 'react-native';
 import { StackNavigator } from 'react-navigation';

class HomeScreen extends Component {
    render() {
    //   const { navigate } = this.props.navigation;
      return (
        <View>
          <Text>Hello, Chat App!</Text>
          <Button
            onPress={() => this.props.navigation.navigate('Chat')}
            title="Chat with Lucy"
          />
        </View>
      );
    }
}

class ChatScreen extends Component {
    render() {
      return (
        <View>
          <Text>Chat with Lucy</Text>
        </View>
      );
    }
}

const Root = StackNavigator({
    Home: {
        screen: HomeScreen,
        navigationOptions: {
            title: 'Home',
        },
    },
    Chat: {
        screen: ChatScreen,
        navigationOptions: {
            title: 'Chat',
        },
    },
  });

  export default Root;

这是整个代码

当我在StackNavigator后加入headerMode:'none',报错没有了，不加又出现，如果没有顶部导航，这个navigator还有啥用，实在没发现那里有问题