validateFields throws an Error if no callback is provided

[Kamahl19]

In the documentation of Ant's Form, there is an example where validateFields is being called without any argument (https://ant.design/components/form/#components-form-demo-horizontal-login)

In this sandbox https://codesandbox.io/s/2wn69y7mqp when you open a console, you can see it's throwing an error because after recent changes in rc-form, callback is being called even though it was not provided.

However when using validateFieldsAndScroll it works fine, because callback is only being called when it exists (here is the check https://github.com/react-component/form/blob/bdbd7b03e88b7d76ad58d39d978e5bce0c7abdf8/src/createDOMForm.js#L93)

I suppose there are 2 solutions:

1. Make callback optional

• add a check typeof callback === 'function' also for the validateFields
• adjust documentation to make it clear that callback is optional

2. Make callback required.

• unify behaviour of validateFields & validateFieldsAndScroll. One throws and one works fine. Both should either print a warning or throw or check or whatever.
• fix Ant's documentation and examples (eg. https://github.com/ant-design/ant-design/blob/65eb713fe897f65bbf187e215c664e5f9b468252/components/form/demo/register.md)
• fix Ant's TS types that allow calling validateFields and validateFieldsAndScroll with no argument (https://github.com/ant-design/ant-design/blob/65eb713fe897f65bbf187e215c664e5f9b468252/components/form/Form.tsx)
• fix Ant's tests (https://github.com/ant-design/ant-design/blob/65eb713fe897f65bbf187e215c664e5f9b468252/components/form/tests/message.test.js#L30)

I know this is not an Ant repo, so please let me know what is the desired solution and I can create a new ticket in Ant repository