Flutter - Base64 class not found

I have a little doubt that maybe you can help me. The problem is the following: I'm creating an entity(Product) in Flutter with local data stored in a json.The entity has three images, which I converted from file to Base64 and put them in the json ... the json grew quite a lot for that reason, but I wanted to reproduce as best as possible the scenario where the application should react once I use a BD SQlite that contains images stored in Base64. As you can see in some examples it is better to declare the attributes where I will save the images as Uint8List and then with the method : Image.memory(product.mainImage) would get the image. But when I try to call the Base64 class I don't find it and when I put the import supposedly where the class is, the VSCode tells me that "import" is not used ... and suggests I remove it. Thank you for your attention and I hope you can help me.

My Json

{
 "products" : [
 {
  "id" : 1, 
  "name":"Perfumes y aseo personal",
  "description" : "Perfumes y aseo personal",
  "mainImage": "/9j/4AAQSkZJRgABAQEAYABgAAD....",
  "firstImage": "/9j/4AAQSkZJRgABAQAAAQABA...",
  "secondImage": "/9j/4AAQSkZJRgABAQEAYABgA..." 
 },
 .....

My Code

import 'dart:async';
import 'dart:typed_data';

class Product {

 int id;
 String name;
 String description;
 Uint8List mainImage;
 Uint8List firstImage;
 Uint8List secondImage;

 Product({this.id,this.name,this.description,this.mainImage,this.firstImage,this.secondImage});

 Product.fromMap(Map<String,dynamic> map)
 :id = map["id"],
  name = map["name"],
  description = map["description"],
  mainImage = No found -> Base64.decode(map["main_image"]), 
  firstImage = No found -> Base64.decode(map["first_image"]),
  secondImage = No found -> Base64.decode(map["second_image"]);

}

You have to import dart:convert and use base64 instead of Base64.