Expected a value of type `undefined` for `author.test` but received `undefined`

'use strict';
const { struct } = require('../lib/superstruct/lib/index');
const Article = struct({
  id: 'number',
  author: {
    id: 'number',
  },
});
const data = {
  id: 34,
  author: {
    id: 1,
    test: undefined,
  },
};
const article = Article(data);
console.log('article', article);

I use the struct to validate data from excel, some unsed keys are set to undefined, and I get an error like : Expected a value of type undefined for author.test but received undefined

I try to partial, but it is not recursive. so I create this issues and a pull request.

[saighost]

ok, maybe I replace struct struct.partial in recursive.

[ianstormtaylor]

@saighost awesome, let us know if you find any issues. Thank you for taking the time to write up that PR either way!