Empty key triggers error in decode-uri-component

[ianwensink]

When you have a query like ?foo=bar&baz, baz won't have a value.

When the values get decoded with decode-uri-component, an error will be thrown:

TypeError: Expected encodedURI to be of type string, got undefined

I think a check should be performed before decoding the value the prevent this error.

[sindresorhus]

We already have a test for this:

query-string/test/parse.js

Lines 59 to 62 in cca7295

	t.deepEqual(queryString.parse('foo=bar&key'), {
	foo: 'bar',
	key: null
	});

Submit a pull request with a failing test and I'll take a closer look.