title: react-navigation@^4 createAppContainer crash with 'Cannot read property getStateForAction of undefined'
body: <p>I tried to run react-navigation v4 on my project however it keeps crashing on launch</p>
  
  <p>I reset cash a hundred times, check every versions are consistent with each others, and follow step-by-step the HelloWorld of react-navigation doc, nothing works even on a simplistic example :</p>
  
  <pre class="lang-js prettyprint-override"><code>import React from 'react';
  import { Text } from 'react-native';
  import { createAppContainer } from 'react-navigation';
  
  import { AppRegistry } from 'react-native';
  import App from './App';
  
  AppRegistry.registerComponent('some-app-name', () =&gt; App);
  
  export default createAppContainer(() =&gt; &lt;Text&gt;LOL&lt;/Text&gt;);
  </code></pre>
  
  <p>Relevant package.json part :</p>
  
  <pre><code>{
  ....
      "react-native": "0.59.10",
      "react-native-gesture-handler": "^1.4.1",
      "react-native-reanimated": "^1.3.0",
      "react-native-screens": "^1.0.0-alpha.23",
      "react-navigation": "^4", // resolving to react-navigation@4.0.10
  ....
  }
  </code></pre>
  
  <p>The error is coming from Component.router which is null in the createAppContainer HOC constructor, specifically:</p>
  
  <p>Error message is "TypeError: Cannot read property 'getStateForAction' of undefined</p>
  
  <p>(from @react-navigation/src/native/src/createAppContainer.js line:131)
  <a href="https://github.com/react-navigation/native/blob/master/src/createAppContainer.js" rel="nofollow noreferrer">https://github.com/react-navigation/native/blob/master/src/createAppContainer.js</a></p>