title: Invariant Violation with only some Navigators (React-Navigation)
body: <p>I'm running into some weird behaviors when trying to implement the Navigators from React-Navigation. </p>
  
  <p>When trying out the simple "hello world" from <a href="https://reactnavigation.org/docs/en/hello-react-navigation.html" rel="nofollow noreferrer">https://reactnavigation.org/docs/en/hello-react-navigation.html</a>...</p>
  
  <pre><code>import React from 'react';
  import { View, Text } from 'react-native';
  import { createStackNavigator } from 'react-navigation';
  
  class HomeScreen extends React.Component {
    render() {
      return (
        &lt;View style={{ flex: 1, alignItems: 'center', justifyContent: 'center' }}&gt;
          &lt;Text&gt;Home Screen&lt;/Text&gt;
        &lt;/View&gt;
      );
    }
  }
  
  export default createStackNavigator({
    Home: {
      screen: HomeScreen,
    },
  });
  </code></pre>
  
  <p>I get this error:</p>
  
  <blockquote>
    <p>Invariant Violation: Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: object.
    Check the render method of 'SceneView'.</p>
  </blockquote>
  
  <p>The strange part is that while using the StackNavigator (and TabNavigator) give me the Invariant Violation, using a DrawerNavigator does not!</p>
  
  <p><a href="https://stackoverflow.com/questions/34130539/uncaught-error-invariant-violation-element-type-is-invalid-expected-a-string">This common fix (removing the braces in the import) gives a new error</a>:</p>
  
  <blockquote>
    <p>Object is not a function</p>
  </blockquote>
  
  <p><a href="https://github.com/react-navigation/react-navigation/issues/666" rel="nofollow noreferrer">And the common fix to "Object is not a function" leads me back to where I started (adding braces to the import).</a></p>
  
  <p>I'm new to React-Native and not sure how to dive deeper into this problem, any help is appreciated!</p>
  
  <p>-----<strong>Edit</strong>-----</p>
  
  <p>I've downgraded my version of react-navigation to v1.5.5 and the original StackNavigator component works, so perhaps it's a compatibility issue with v2.0.1 and my environment.</p>