Node-style callback in TypeScript with Nullthrows

CallbackNullthrows.ts

import Nullthrows from "@makepost/nullthrows";

class Post {
  id = "";
}

interface ICallback<T> {
  (error: Error, _?: undefined): void;
  (_: undefined, post: T): void;
}

const callback: ICallback<Post> = (error?: Error, post?: Post) => {
  if (error) {
    console.error(error.message);
  } else {
    console.log(Nullthrows(post).id);
  }
};

callback(undefined, new Post());
callback(new Error("Unauthorized"));