Typescript: Intellisense not working with union type

[WilliamChelman]

• VSCode Version: 1.23.1
• OS Version: Pop!_OS 17.10

Steps to Reproduce:

1. Create a typescript file and try the following. When the type is "unioned" with undefined, the autocomplete cannot advise to use the enum anymore.
   

2. This is most annoying with situations like this, with optional parameters given to functions.
   

Does this issue occur when all extensions are disabled?: Yes

[mjbvz]

This issue was moved to microsoft/TypeScript#24304