fix: Update ChangeStream hydration condition

[ramos-ph]

Summary

There is an issue when using a ChangeStream in a replica set, you'll get an undefined error when you try to call mongoose.disconnect():

await mongoose.connect(`mongodb://${host}:${port}/?replicaSet=${rset}`, {
  autoIndex: false,
});

const changeStream = mongoose.connection.watch(pipeline, {
  fullDocument: "updateLookup",
});
const stream = changeStream.on("change", (change) => {
  console.log(change);
});

await stream.close();
await mongoose.disconnect(); // `data.fullDocument` is undefined

The issue was introduced in one of the commits from versions 6.4.7 to 6.5.0, as stated in #12169. This PR fixes this by correctly addressing where the options are coming from.

Examples

Here's the result for the current version:

Here's the result for the fix:

Closes #12169

[vkarpov15]

Why not just add if (data != null && data.fullDocument != null && ...) ?

[vnugent]

Hi,
when do you think we have this released?
I did a quick test. The issue still exists in 6.5.1

upgrading mongoose

-    "mongoose": "6.4.7",
+    "mongoose": "6.5.1",

[vkarpov15]

I think this was also fixed in #12224, but we'll merge this one as well. Will ship a release with the fix within 24 hours 👍