CreateSession function of Adapter does not provide userId in the session object

[stuvan]

This is how I am setting up auth.js "5.0.0-beta.21" with database strategy

import NextAuth from "next-auth";
import Discord from "next-auth/providers/discord";
import { CustomAdapter } from "./lib/Adapter/CustomAdapter";

const Auth = NextAuth({
  providers: [Discord],
  adapter: CustomAdapter(),
  session: {
    strategy: "database",
  },
});

export const { handlers, signIn, signOut, auth } = Auth;

export default Auth;

Created a custom adapter where createSession function defined like this

 // Sessions
    createSession: (session) => {
      console.log("create session -----------------------");
      console.log(session);
      return { userId: "asdf", expires: new Date(), sessionToken: "213" };
    },

The userId of the session object is undefined?

How can I create a session in database if the id of the user is undefined?