Formik should gracefully handle onChange without a valid event

[ajsharp]

🐛 Bug report

Current Behavior

Some libraries like downshift.js don't give you a native event in the change handler. I'm not a fan of this design decision but it is what it is. So if I manually call onChange on a formik Field with an event, it blows up on this line when it tries to destructure event.target.:

formik/packages/formik/src/Formik.tsx

Line 592 in c959f47

const {

This is the error: Cannot read property 'type' of undefined

So, what I'm doing currently is just passing in an empty target object, and it seems to solve the problem.

Expected behavior

If the code above didn't explode, and instead gracefully handled a null object in event.target.

Reproducible example

https://codesandbox.io/s/formik-codesandbox-template-xnfxx

Suggested solution(s)

Gracefully initialize an empty object if it doesn't exist.

Your environment

Software	Version(s)
Formik	2.1.0
React	16.12.0
Browser	Chrome Version 79.0.3945.117
npm/Yarn
Operating System	Mac OS

[jaredpalmer]

This is a 4th or 5th issue around handleChange / event handling / currying since v2. Going to make an umbrella so we can centralize and then debate next steps to minimize api churn

[walkerdb]

@jaredpalmer I think the main cause of these issues is that v1 technically allowed any object type to be passed in to handleChange, eg this else clause when the value isn't a react event: https://github.com/jaredpalmer/formik/blob/v1.5.8/src/Formik.tsx#L338 .

In v2 this was changed to only accept either a string or a react event, and assumes that any input that isn't a string is a react event, which will break the forms of anyone who happened to be using it assuming it could take any value. This doesn't seem to currently be mentioned as a breaking change in the migration docs.