I can’t find a way to set a field with type ObjectId to null after giving it a value

Exemple :
UserModel.ts

const UserSchema = new Schema({
  userId: {type: String, required: true}
  guild: {type: Schema.Types.ObjectId, ref: "guilds", default: null}
});

type User = InferSchemaType<typeof UserSchema>;

export default model<User>("users", UserSchema);

When my user join a guild i can simply do

index.ts

import userSchema from ./UserModel.ts

const user = await userSchema.findOne(query);
user.guild = // a guild object id (_id)
await user.save()

But when my user want to leave one I can’t set it back to null
index.ts

import userSchema from ./UserModel.ts

const user = await userSchema.findOne(query);
user.guild = null
await user.save()

I get this error -> Type 'null' is not assignable to type 'ObjectId'

Is it possible or a limitation of mongoose ?

I’ve tried to infer null or undefined to the guild field

UserModel.ts

const UserSchema = new Schema({
  userId: {type: String, required: true}
  guild: {type: Schema.Types.ObjectId, ref: "guilds", default: null}
});

type Hunter = InferSchemaType<typeof hunterSchema> & {
  guild: Types.ObjectId | null | undefined;
};

export default model<User>("users", UserSchema);