How to Represent a Union Type in Dart Similar to TypeScript for Creating a Data Class with json_serializable?

I am currently working on a Flutter project where I am trying to create a data class for a User that involves an Image property. In TypeScript, I have a union type Image that can be either a boolean or an array of { quality: string; link: string } objects. Here is the TypeScript example:

type Image = boolean | {
  quality: string;
  link: string
 }[];

type User = {
  id: string;
  name: string;
  image: Image;
};

const user1: User = {
  id: "1",
  name: "John Doe",
  image: false,
};

const user2: User = {
  id: "1",
  name: "John Doe",
  image: [
    {
      quality: "small",
      link: "https://example.com/image1",
    },
    {
      quality: "medium",
      link: "https://example.com/image2",
    },
    {
      quality: "large",
      link: "https://example.com/image3",
    },
  ],
};

Now, I want to create a similar data class for User in Dart to facilitate JSON serialization and deserialization using json_serializable.

How can I represent this union type in Dart while keeping in mind that I want to use json_serializable to generate the serialization/deserialization code for my data class? I want to have a more precise type definition for the Image property to handle both boolean and array cases appropriately.

Any help, code samples, or guidance would be greatly appreciated. Thank you!