Working with optional attributes in JSON is quite inconvenient to write:

Stream stream = {
    appId : js["appId"].str,
    // like this
    appVersion : js.object.get("appVersion", JSONValue("")).str,
    // or that
    startTimestamp : ("startTimestamp" in js is null) ? "" : js["startTimestamp"].str,
};


Adding opt* methods like optStr(string key, defaultValue = string.init) would make the usage a lot more readable:

Stream stream = {
    appId : js["appId"].str,
    appVersion : js.optStr("appVersion", "1.0"),
    startTimestamp : js.optStr("startTimestamp")
};