First, thank you @philipstanislaus for building this nice and helpful tool!

I ran in some issues while trying to use it on a project, which I could track down to these points:

• Items are ignored, if their parentId is undefined.
• Items are ignored, if their parentId is 0.

Looking at the code, I saw, that you expect IDs to be strings. My project uses Integers with parentId: 0 for Root-Items. So no surprise it didn’t work out.

Would you mind:

• adding support for Integer IDs?
• allowing undefined (= nonexisting) and 0 (Int) as values of parentId in addition to null?

I would submit a PR, but I’m not used programming in TypeScript. :) Thank you in advance.