avatar must be a string (was undefined) although undefined it expected type

import { type } from "arktype";

export const profileData = type({
    firstName: 'string',
    lastName: 'string',
    'avatar?': 'string'
});
export type ProfileData = typeof profileData.infer

const data = profileData.partial()({ firstName: 'John', lastName: 'Doe' });

const data = profileData.partial()({
  firstName: 'John', 
  lastName: 'Doe',
  avatar: undefined
});

const data: ArkErrors | {
    firstName?: string | undefined;
    lastName?: string | undefined;
    avatar?: string | undefined;
}