问react本机中的CreateStackNavigator返回null

EN

import { createStackNavigator } from "react-navigation-stack";
import { createAppContainer } from "react-navigation";
import { Home } from "../components/Home";
import { Test } from "../components/Test";

const screens = {
  home: {
    screen: Home
  },

  test: {
    screen: Test
  }
};

const HomeStack = createStackNavigator(screens);

export default createAppContainer(HomeStack);

/**
 * Sample React Native App
 * https://github.com/facebook/react-native
 *
 * @format
 * @flow
 */

import React, { Component } from "react";
import {
  StyleSheet,
  ScrollView,
  View,
  Text,
  StatusBar,
  Button
} from "react-native";

import Navigator from "./routes/homeStack";

export class App extends Component {
  constructor() {}

  render() {
    return <Navigator />;
  }
}

const styles = StyleSheet.create({});

import React, { Component } from "react";
import {
  StyleSheet,
  ScrollView,
  View,
  Text,
  StatusBar,
  Button
} from "react-native";
import { About } from "./About";
import { Contact } from "./Contact";

export class Home extends Component {
  constructor() {
    super();
  }

  render() {
    return (
      <>
        <View>
          <Text>This is Home Component</Text>
        </View>
        <Button
          title="navigate to Test"
          onPress={() => this.props.navigation.navigate("test")}
        ></Button>
      </>
    );
  }
}

import React, { Component } from "react";
import {
  StyleSheet,
  ScrollView,
  View,
  Text,
  StatusBar,
  Button
} from "react-native";

export class Test extends Component {
  constructor() {
    super();
    this.state = {
      something: "This is Test Component"
    };
  }

  render() {
    return (
      <>
        <View>
          <Text>this.state.something</Text>
        </View>
        <Button
          title="navigate to Home"
          onPress={() => this.props.navigation.navigate("home")}
        ></Button>
      </>
    );
  }
}

{
  "name": "reviewsApp2",
  "version": "0.0.1",
  "private": true,
  "scripts": {
    "android": "react-native run-android",
    "ios": "react-native run-ios",
    "start": "react-native start",
    "test": "jest",
    "lint": "eslint ."
  },
  "dependencies": {
    "@react-native-community/masked-view": "^0.1.5",
    "react": "16.9.0",
    "react-native": "0.61.5",
    "react-native-gesture-handler": "^1.5.3",
    "react-native-reanimated": "^1.4.0",
    "react-native-safe-area-context": "^0.6.2",
    "react-native-screens": "^2.0.0-alpha.23",
    "react-navigation": "^4.0.10",
    "react-navigation-stack": "^2.0.2"
  },
  "devDependencies": {
    "@babel/core": "^7.6.2",
    "@babel/runtime": "^7.6.2",
    "@react-native-community/eslint-config": "^0.0.5",
    "babel-jest": "^24.9.0",
    "eslint": "^6.5.1",
    "jest": "^24.9.0",
    "metro-react-native-babel-preset": "^0.56.0",
    "react-test-renderer": "16.9.0"
  },
  "jest": {
    "preset": "react-native"
  }
}