title: React Native - There is no route defined for Login
body: <p>I'm learning react native with configuring tabNavigator, DrawerNavigator, and StackNavigator into one without NativeBase or Expo with a single react-navigation library.</p>
  <p>I achieved it but there comes an error when I perform some specific sequence in my application.</p>
  <p>The application starts with Tab Screen. -&gt; Change Tab -&gt; Open Drawer -&gt; Goto Stack -&gt; open Drawer and then go to Tabs gives this error.</p>
  <p>Here is my code :</p>
  <p><strong>App.js</strong></p>
  <pre><code>import React from 'react';
  import {Drawer} from &quot;./src/navigation/MergedNavigator&quot;;
  import {View,Text} from &quot;react-native&quot;;
  
  const App = () =&gt; (
      &lt;View style={{flex: 1,backgroundColor: '#293656'}}&gt;
          &lt;Drawer /&gt;
      &lt;/View&gt;
  );
  
  export default App;
  </code></pre>
  <p><strong>MergedNavigator.js</strong></p>
  <pre><code>import {DrawerNavigator,StackNavigator,createBottomTabNavigator} from 'react-navigation';
  
  // stack navigation screens
  import DetailScreen from '../screens/detail';
  import MainScreen from '../screens/main';
  import ForgotScreen from '../screens/ForgotScreen';
  import RegisterScreen from '../screens/RegisterScreen';
  
  // tab navigator screens
  import LoginScreen from '../screens/Login';
  import TabOne from '../screens/tabA';
  import TabTwo from '../screens/tabB';
  
  //plain
  
  export const stack = StackNavigator({
      DetailScreen:{screen:DetailScreen},
      MainScreen:{screen:MainScreen}
  },{
      initialRouteName:'DetailScreen'
  });
  
  const secondStack = StackNavigator({
      RegisterScreen:{screen:RegisterScreen},
      ForgotScreen:{screen:ForgotScreen}
  },{
      initialRouteName:'ForgotScreen'
  })
  
  export const Tabs = createBottomTabNavigator({
      Login:{screen:LoginScreen},
      TabOne:{screen:secondStack},
      TabTwo:{screen:TabTwo}
  },{
      animationEnabled:true
  })
  
  export const Drawer = DrawerNavigator({
      Tabs:{screen:Tabs},
      Stack:{screen:stack}
  })
  </code></pre>
  <p>And all other imported stack screen has nothing but the title.
  What's the problem here with my code? Or is there any better way I can achieve these all 3 Navigators with only react-navigation?</p>