Incorrect Typings: array.ensure() should not produce undefined

[denis-pakhorukov]

Describe the bug
According to the documentation, array.ensure() sets the default to [] and transforms null and undefined values to an empty array. However, the typings imply that undefined is still a possible value.

To Reproduce

import * as Yup from "yup";

const userSchema = Yup.object().shape({
  array1: Yup.array().of(Yup.string().required()),
  array2: Yup.array().of(Yup.string().required()).default([]),
  array3: Yup.array().of(Yup.string().required()).ensure(),
});

type User = Yup.InferType<typeof userSchema>;

Actual behavior

type User = {
    array1?: string[] | undefined;
    array2: string[];
    array3?: string[] | undefined;
}

Expected behavior

type User = {
    array1?: string[] | undefined;
    array2: string[];
    array3: string[];
}