Typescript: Also allow undefined for `Option<T>`?

currently its translated to `T | null`, which is not very convenient for functions with optional arguments.
actually it already accepts `undefined`, just the typescript types don't allow it yet.

example:
```js
// in js I can do:
await client.getChatlistEntries(3)
// but in ts I need to do this:
await client.getChatlistEntries(3, null, null, null)
```