nil

If you use the nil modifier, given schema will be extended to also match null and undefined values, and its output type will be null | undefined | T.

const nilRoleSchema = nil(oneOf(['User', 'Admin']));

const nilRoleValidator = validate(nilRoleSchema);

// Returns 'User', the output type is undefined | null | 'User' | 'Admin'

const role = nilRoleValidator('User');

// Both return undefined

nilRoleValidator();

nilRoleValidator(undefined);

// Returns null

nilRoleValidator(null);