Manual json deserialization in dart

class Content {
final String title;
final String description;
final String video_url;
final String video_title;

Content({this.title,this.description,this.video_url,this.video_title});
factory Content.fromJson(Map<String dynamic> json){
    return Content (
        title:json['title']??'',
        description:json['description']??'',
        video_url:json['video_url']??'',
        video_title:json['video_title']??'',
        );
    }
}

class Course {
final String image_url;
final String name;
final List<Content> contents;
Course({this.image_url,this.name,this.contents});

factory Course.fromJson(Map<String dynamic> json){
    return Content (
        name:json['name']??'',
        image_url:json['image_url']??'',
        contents:json['contents']?json['contents'].map((c){ return Content.fromJson(c);}).toList() :[],
        );
    }
}

}