Type definition of FormikErrors should allow nulls

[KrzysztofMadejski]

🐛 Bug report

Current Behavior

If we are validating a value being a list (ie. supported by FieldArray) then some errors on the list might be null (ie. [null, "error"]), but current typescript definitions don't allow for that.

Expected behavior

Following code (along sandbox don't produce typescript compiler errors):

setErrors({friends:[null,{"name":"too short"}]})

Reproducible example

https://codesandbox.io/s/formik-fieldarray-sb4ql

Suggested solution(s)

formik/src/types.tsx

Lines 13 to 21 in 5c59dbe

	export type FormikErrors<Values> = {
	[K in keyof Values]?: Values[K] extends any[]
	? Values[K][number] extends object // [number] is the special sauce to get the type of array's element. More here https://github.com/Microsoft/TypeScript/pull/21316
	? FormikErrors<Values[K][number]>[] | string | string[]
	: string | string[]
	: Values[K] extends object
	? FormikErrors<Values[K]>
	: string;
	};

should allow nulls in array of errors:

export type FormikErrors<Values> = {
  [K in keyof Values]?: Values[K] extends any[]
    ? Values[K][number] extends object // [number] is the special sauce to get the type of array's element. More here https://github.com/Microsoft/TypeScript/pull/21316
      ? (FormikErrors<Values[K][number]>|null)[] | string | (string|null)[]
      : string | (string|null)[]
    : Values[K] extends object
    ? FormikErrors<Values[K]>
    : string;
};

Your environment

Software	Version(s)
Formik	2.0.6