TypeScript Version: 2.4.1-dev.20191120 (nightly)

TS2532
Object is possibly undefined
Narrow

Code

interface Version {
  createdAt: string
}

const stuff = (version?: Version, createdAt?: string) => {
  if (!(createdAt || version)) {
    return null;
  }

  return createdAt || version.createdAt;
};

Expected behavior:
version should be narrowed as defined.

Actual behavior:
version still considered possibly undefined.

(parameter) version: Version | undefined
Object is possibly 'undefined'.(2532)

Playground Link:
https://typescript-play.js.org/#code/JYOwLgpgTgZghgYwgAgGrQM7APYmQbwChlkEoI5IATAQTAC5kMwpQBzQgX0MIV2aZgArjBjIAvMgAUAN0w4QAfkbooWXABpS5ShFphlg1iDYBKCQD4CxZMDFSAhFLIVqdZAB8PyOWoWnzIhIScmEoPBAhABsogG4bbhtQoXDtVz13Lx95XAA6F119eM54oA