Can't assign to conditional generic within generic

[ayroblu]

Hi I was trying to do something much more complicated than this with conditionals without success, I was reducing the issue down and down and I found this, which I find a bit weird, I was hoping someone might be able to enlighten me of a work around?

TypeScript Version: v4.1.2

Search Terms:
assign to conditional generic

Code

type Param<T> = T extends undefined ? {
    first: string,
} : {
    first: string,
}
function run<T>(param: T) {
    const p: Param<T> = {
        first: 'hi'
    }
    return p;
}

Expected behavior:
No type error

Actual behavior:
type error

Playground Link:
link here

Related Issues:
I couldn't find any, sorry if this is a well known problem / duplicate!

[MartinJohns]

Duplicate of #26933. Search terms used: assign conditional