optional() on an object field makes it required

[typeofweb]

Describe the bug
Consider these two schemas:

import * as Yup from "yup";

const schemaWorking = Yup.object({
  field: Yup.boolean()
});
const schemaBroken = Yup.object({
  field: Yup.boolean().optional(),
});

Both should validate an empty object {} just fine given that the field is optional in both of them. Unfortunately, that's no the case. Adding .optional() call in the second schema actually makes the field required.

To Reproduce

https://codesandbox.io/s/cool-almeida-7ds47t

import * as Yup from "yup";

const schemaWorking = Yup.object({
  field: Yup.boolean()
});
const schemaBroken = Yup.object({
  field: Yup.boolean().optional(),
});

schemaWorking.validateSync({ });
schemaBroken.validateSync({ });

Expected behavior
Both schemas validate an empty object just fine.

Platform (please complete the following information):

• Version 1.0.0-beta.3 (same problem on master)

[jquense]

thanks for bug report. It's actually just booleans that are affected by this and will be fixed in the next release