What

I suggest to make the return statement of form.submit() unified for all its branching.

Why

Current behavior

Now calling form.submit() returns two different things based on the validity of a form:

1. Returns undefined if a form is invalid.
2. Returns Promise<response> after the dispatched action.

Expected behavior

Calling form.submit() always returns

To allow support for:

string().in('foo', 'bar');
string().in(['foo', 'bar']);