I have this (simplified version of) function

function empty(value: unknown) {
  return value === undefined || value === null;
}

which I’m calling in another function

function foo(user) {
  if (empty(user)) return;
  console.log(user.id); // error
}

I’m getting a error 'user' is possibly 'undefined'.ts(18048) error.

How can I make foo (or any other function using empty) know that the type is safe after checking with empty. Without using assertions like console.log((user as User).id);