title: Could not find a generator for route RouteSettings("/", null) in the _WidgetsAppState
body: <p>I'm writing a <code>Flutter</code> app (Kinda a beginner here). Here is my code.<br>
  <code>main.dart</code>  </p>
  
  <pre><code>import 'package:flutter/material.dart';
  import 'package:flutter_app_timer/helpers/constants.dart';
  
  void main() =&gt; runApp(ContactApp());
  
  class ContactApp extends StatelessWidget {
    @override
    Widget build(BuildContext context) {
      return MaterialApp(
        debugShowCheckedModeBanner: false,
        title: appTitle,
        theme: new ThemeData(
          primaryColor: appColor,
        ),
      );
    }
  
  }  
  </code></pre>
  
  <p><code>constants.dart</code>  </p>
  
  <pre><code>import 'package:flutter/material.dart';
  
  Color appColor = Color.fromRGBO(58, 66, 86, 1.0);
  
  const appTitle = "Contact App";  
  </code></pre>
  
  <p>When I run it in emulator, I get below exception message.  </p>
  
  <blockquote>
    <p>I/flutter ( 7381): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY  ╞═══════════════════════════════════════════════════════════<br>
    I/flutter ( 7381): The following assertion was thrown building IconTheme(IconThemeData#2abdc(color:<br>
    I/flutter ( 7381): Color(0xdd000000))):<br>
    I/flutter ( 7381): Could not find a generator for route RouteSettings("/", null) in the _WidgetsAppState.  </p>
  </blockquote>
  
  <p>Do I need to add <code>Navigator</code> in <code>main.dart</code>? How can I fix this?   </p>