Re: [mediacapture-screen-share] Address nullability of DisplayMediaStreamOptions.controller (#236)

To understand the general advice here better, is it meant to also apply to dictionary arguments to constructors?

I notice in both this and the AddEventListenerOptions example, there were no corresponding `readonly` attribute exposing the internal slot for JS to read back what was set, if anything (is the advice for such an attribute to still yield `null`, or `undefined`)? Interfaces don't support missing AFAIK). If the answer is the readonly attribute should be `null`, then not accepting `null` as input would seem mildly unexpected perhaps, and also break any (encouraged or discouraged?) constructor duplicator patterns popularized by Events., and used in places like RTCSessionDescription E.g.
```js
const a = new Foo({bar: new Bar()})
const b = new Foo({});
const c = b.bar; // null or undefined?
const d = new Foo(b); // b is member equivalent and has toJSON(), but TypeError over b.bar being null?
```

-- 
GitHub Notification of comment by jan-ivar
Please view or discuss this issue at https://github.com/w3c/mediacapture-screen-share/issues/236#issuecomment-1264385914 using your GitHub account


-- 
Sent via github-notify-ml as configured in https://github.com/w3c/github-notify-ml-config