We must always return at least some validation rule. So first off if value !== undefined then we'll return our previous validation schema. If it is undefined then we'll use the yup.mixed().notRequired() which will just inform yup that nothing is required at the optionalObject level. optionalObject: yup.lazy(value => { if (value !== undefined) { return yup.object().shape({ otherData: yup.string().required(), }); } return yup.mixed().notRequired(); }),

passing the context into validateSync()

Yup.ref('value')