An empty string is considered as a valid email

Describe the bug

yup.string().email().validateSync('') throws no errors and returns an empty string.

And

var yup = require("yup")

const schema =  yup.object().shape({
    email: yup.string().email(),
});

schema.validateSync({email: ''})

Also works without errors.

To Reproduce

Just run the code

var yup = require("yup")
yup.string().email().validateSync('')

const schema =  yup.object().shape({
    email: yup.string().email(),
});

schema.validateSync({email: ''})

here https://npm.runkit.com/yup

Expected behavior

An error that the email is invalid must be thrown.

Platform (please complete the following information):

Node.js 10.15.0

[jquense]

an empty string is considered a missing value for strings, so most validations besides required ignore it. If you want to check empty strings as invalid, mark the field as required as noted above thanks!

[RussCoder]

@akmjenkins You should read my previous message again and run the code:

const schema =  yup.object().shape({
    email: yup.string().required().email(),
    name: yup.string().ensure(),
    lastname: yup.string().ensure(),
});

const res = schema.validateSync({name: 'ads'}, {
    strict: true, 
    abortEarly: false, 
    stripUnknown: true
});

Email isn’t a required field for me.