Json.undefined serializes to invalid Json

[tchaloupka]

This is related to: #1442

auto json = Json();
writeln(json.serializeToPrettyJson);

Json should allways serialize to a valid Json I think. So probably to null in this case?

[dcousens]

undefined is not valid JSON, tbh, I'm not sure why vibe.d even included it seeing as Json.emptyObject["foobar"] != Json.undefined

[thaven]

Json.undefined may be returned when referencing a key that is not present in a Json object. It should not be serialized to anything, except when at the root of the tree, then it should be serialized as null.

[dcousens]

@thaven except Json.undefined != Json.undefined

[thaven]

@dcousens One may argue if two non-existing 'things' should be considered equal... ;-) That is probably why the type of the Json object is being compared to Json.Type.undefined.

[dcousens]

@thaven in JS, undefined === undefined, fwiw