Using a mapped type, can't Exclude "undefined" from an optional property #24067

type NeverUndefined<T> = {
    [K in keyof T]: Exclude<T[K], undefined>;
}

interface MyInterface {
    undef: undefined
    optionalString?: string;
    stringOrUndefined: string | undefined;
    definedString: string;
}

type NeverUndefinedMyInterface = NeverUndefined<MyInterface>;

// typeof NeverUndefinedMyInterface
interface NeverUndefinedMyInterface {
    undef: never;
    optionalString: string;
    stringOrUndefined: string;
    definedString: string;
}

// typeof NeverUndefinedMyInterface
interface NeverUndefinedMyInterface {
    undef: never;
    optionalString: string | undefined;
    stringOrUndefined: string;
    definedString: string;
}