Type errors when using optional typed children

[tomdye]

bug

When typing optional children as follows:

type HelloChildRenderer = () => RenderResult;

const factory = create()
  .properties<HelloProperties>()
  .children<HelloChildRenderer | undefined>();

I am given a type error if I try to create the Hello widget using a self closing tag or without passing children. It appears that passing an empty {} child or {undefined} works but this is not ideal.

Please see linked codesandbox example:
https://codesandbox.io/s/dojo-codesandbox-template-eshg6