title: Expected a value of type 'Widget', but got one of type 'Null'
body: <p>i am learning responsive web but i am stuck here in some kind of error like</p>
  <blockquote>
  <p>Expected a value of type 'Widget', but got one of type 'Null'</p>
  </blockquote>
  <p>don't know how to fix this error i tried a lot but i think i can't solve this without someone's help.</p>
  <pre><code>import 'package:flutter/material.dart';
  
  const int largeScreenSize = 1366;
  const int mediumScreenSize = 768;
  const int smallScreenSize = 360;
  const int customScreenSize = 1100;
  
  class Responsiveness extends StatelessWidget {
     final Widget? largeScreen;
     final Widget? mediumScreen;
     final Widget? smallScreen;
  
     const Responsiveness({
      this.largeScreen,
      this.mediumScreen,
      this.smallScreen,
    });
  
     @override
     Widget build(BuildContext context) {
       return LayoutBuilder(builder: (context, constraints) {
         double _width = constraints.maxWidth;
          if (_width &gt;= largeScreenSize) {
           return largeScreen as Widget;
         } else if (_width &gt;= mediumScreenSize &amp;&amp; _width &lt; largeScreenSize) {
           return mediumScreen ?? largeScreen as Widget;
         } else {
           return smallScreen ?? largeScreen as Widget;
         }
       });
     }
   }
  </code></pre>