title: how to Use class as datatype in dart Parse Json
body: <p>I have Main class this is called FullTrip this class has attributes called itineraries and others contain two pieces of data <br />
  so i create another class called Hc  now i need to use this combination two parse json response from the server</p>
  
  <pre><code>class FullTrip extends Trip{
  
    final List&lt;String&gt; including;
    final List&lt;String&gt; excluding;
    final List&lt;Hc&gt; itineraries;
    final List&lt;Hc&gt; policies;
  
    FullTrip(this.including,this.excluding,this.itineraries,this.policies,int id,String title,double price,String overview,String hero_image): 
    super(id:id,title:title,price:price,overview:overview,hero_image:hero_image);
  
  
      factory FullTrip.fromJson(Map&lt;String, dynamic&gt; json) =&gt; 
          _$FullTripFromJson(json);
  }
  
    class Hc {
      final String head;
      final String content;
      Hc({this.head,this.content});
    }
  </code></pre>
  
  <p>when i use the code like that and run serialization command <br /></p>
  
  <pre><code>flutter packages pub run build_runner build --delete-conflicting-outputs
  </code></pre>
  
  <p>i got error in terminal</p>
  
  <blockquote>
    <p>[SEVERE] json_serializable on lib/models/fulltrip.dart: Error running
    JsonSerializableGenerator Could not generate <code>fromJson</code> code for
    <code>itineraries</code> because of type <code>Hc</code>. None of the provided <code>TypeHelper</code>
    instances support the defined type.
    package:Tourism/models/fulltrip.dart:21:18   final List
    itineraries;
                     ^^^^^^^^^^^ [WARNING] json_serializable on lib/models/fulltrip.dart: Missing "part 'fulltrip.g.dart';". [INFO]
    Running build completed, took 3.0s</p>
    
    <p>[INFO] Caching finalized dependency graph... [INFO] Caching finalized
    dependency graph completed, took 68ms</p>
  </blockquote>