[BUGFIX beta] Improve behavior for QPs with undefined values

[trentmwillis]

For the case of lazy loading Engines, all QPs get serialized into the URL initially. undefined shouldn't get serialized to a string, so that when it gets pulled out the value is not a string.

cc @nathanhammond

[nathanhammond]

People willing to make hard decisions: can we take this a step further? I'd like to force all values passed into queryParams to be JSON serializable.

 _serializeQueryParams(handlerInfos, queryParams) {
  queryParams = JSON.parse(JSON.serialize(queryParams));
  // ...

This makes it possible for people to either pass arbitrary objects which implement toJSON as values to keys and also sets us up well for a world in which we do structured query params.

It also neatly sidesteps this issue:

JSON.parse(JSON.stringify({foo:undefined}));
// => {}
JSON.parse(JSON.stringify({foo:null}));
// => { foo: null }

Thoughts?

[rwjblue]

Looks good to me, with one small nit-pick...

[rwjblue]

Super not-picky but I'd rather leave this as an unconditional else clause. Could you swap this to check if it's undefined and just noop (as an else if before the final else)?

[rwjblue]

@nathanhammond - Let's keep that separate from this PR, but generally I think it could work (generally speaking). Happy to review a PR (or general sketch of the logic).

[trentmwillis]

@rwjblue updated, but getting a linting error. Should I just return from the block?

[rwjblue]

Thanks @trentmwillis!