title: Why am I getting undefined is not an object (evaluating 'ReactPropTypes.string') error?
body: <p>Here's the thing, I'm dealing with like 10 <code>.js</code> files so posting them here would be way too much.  My question is, what are the possible reasons I'm getting this error?  I understand it's somewhat of a vague question, but I can't find an answer anywhere to this. </p>
  
  <p>On top of this, there are absolutely no errors in any of these <code>.js</code> files.  It's only when I hit <code>Run</code> to see the result of my code in the simulator do I see the error (pic below).  </p>
  
  <p>My apologies again if it's too vague, I just don't know where else to turn.</p>
  
  <p>Could it be in this file?  I think it's all correct here.  I just have a slight feeling this file is the problem.</p>
  
  <p>Here's <code>Router.js</code></p>
  
  <pre><code>import React, { Component } from 'react';
  import { Navigator } from 'react-native';
  import Home from './Home';
  import Location from './Location';
  import Interest from './Interest';
  import Login from './Login';
  import Signup from './Signup';
  
  export default class Router extends Component {
    constructor() {
      super();
    }
  
    configureScene(route, routeStack) {
      return Navigator.SceneConfigs.FloatFromBottomAndroid;
    }
  
  renderScene(route, navigator) {
    if (route.name === 'Home') {
      return (
        &lt;Home
        navigator={navigator}
        {...route.passProps}
        /&gt;
      );
    }
    if (route.name === 'Location') {
      return (
        &lt;Location
        navigator={navigator}
        {...route.passProps}
        /&gt;
      );
    }
    if (route.name === 'Interest') {
      return (
        &lt;Interest
        navigator={navigator}
        {...route.passProps}
        /&gt;
      );
    }
    if (route.name === 'Login') {
      return &lt;Login navigator={navigator} {...route.passProps} /&gt;
    }
    if (route.name == 'Signup') {
        return ( &lt;Signup navigator={navigator} {...route.passProps} /&gt; )
      }
  }
  
  render() {
    return (
      &lt;Navigator
        configureScene={this.configureScene}
        initialRoute={{ name: 'Home', title: 'Home' }}
        renderScene={this.renderScene}
      /&gt;
    );
  }
  
  }
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/lHTVD.png" rel="nofollow noreferrer">Weird error</a></p>