Change the treatment of falsy values in _.toQuery and _.fromQuery?

@yashshah1 pointed out a problem with _.toQuery and _.fromQuery: through stringification, falsy values are being "upgraded" to truthy if you encode them and then decode them again. For example, _.fromQuery(_.toQuery({a: null})) returns {a: 'null'}.

@yashshah1 proposed the following solution in https://github.com/documentcloud/underscore-contrib/pull/229#issuecomment-683548408:

What I am suggesting is a change in both toQuery and fromQuery.

Proposed behaviour:

_.toQuery('{ a: '', b: null, c: undefined, d: '10' }')
// a=&b=&d=10

_.fromQuery('a=&b=&d=10')
// { a: '', b: '', d: '10' }

Reasoning
The idea is that toQuery and fromQuery need to be as complementary to each other as possible, one drawback that's seen already is that numbers need to be re-parsed. Wrt falsy values, however, I think there has to be a special provision as described above.

What we gain by this is that null values are re-encoded as empty strings, which is falsy, and undefined isn't included in the object, which leads to almost the same usage in a few cases.

var obj = { a: '', b: null, c: undefined, d: '10' }
console.log(obj['c']) // undefined

obj = _.fromQuery(_.toQuery(obj))
console.log(obj['c']) // undefined

This might lead to a change in the behaviour of fromQuery and I am happy to raise a PR should this be acceptable.

I'm not sure whether this approach would be the right solution, for a couple of reasons:

• Information loss: undefined, null and the empty string '' could no longer be distinguished.
• What to do with numeric zero?
• How does this align with jQuery's encoding conventions?

However, this is something we can discuss. Let's do that here.

Start with the _.toQuery and _.fromQuery entry points and review the linked pull-request discussion. Decide how null, undefined, empty strings, and numeric zero should round-trip, including whether jQuery conventions apply. Done means an agreed behavior is documented and both functions have coverage for the selected cases.