email or empty string not working

export const feedbackSchema = type({
    contact: 'string.email | string == 0'
});

export const feedbackSchema = type({
    contact: 'string.email | string == 0'
});

Is giving runtime error:

ParseError: Key $ is not valid on maxLength schema

ParseError: Key $ is not valid on maxLength schema

but it works with just

string.email

string.email

email or empty string not working - arktype