Why is User.id optional?

[musjj]

Is there a reason why User.id optional?

next-auth/packages/core/src/types.ts

Lines 261 to 266 in 1817273

	export interface User {
	id?: string
	name?: string | null
	email?: string | null
	image?: string | null
	}

According to this, all providers should be able to provide an id:

next-auth/packages/core/src/types.ts

Lines 125 to 130 in 1817273

	* This value depends on the type of the provider being used to create the account.
	* - oauth/oidc: The OAuth account's id, returned from the `profile()` callback.
	* - email: The user's email address.
	* - credentials: `id` returned from the `authorize()` callback
	*/
	providerAccountId: string

So in what situation does id become undefined?