findOneAndUpdate typing does not include null result

[janeisenmenger]

This issue occurred when updating from 6.0.5 to 6.0.8

The behaviour before was that findOneAndUpdate would either return the new/old document (depending on the options) or null, when no document was updated.
With this commit the typing of the function was changed to not include null anymore.

However, it is still possible to receive a null value, regardless of the typing. Steps to reproduce:

• call findOneAndUpdate on an empty repository (any data or model will do)
• Check the return value -> This is were we receive null, even though it shouldn't be according to the typing.

My proposition would be to add the null value back to the typing or throw a matching error.

Versions used:

• Node.js: 14.17.5
• MongoDB: 4.2
• Mongoose: 6.0.8

[IslandRhythms]

Where does it say on the doc pages that null is not a possible value?

[janeisenmenger]

Hey @IslandRhythms!
The documentation doesn't mention null on the corresponding findOneAndUpdate page, or at least I couldn't find it.
Regardless of the documentation, I think the typing should reflect the return values the function could have, and currently it does not.
So: When looking at the typing of Model.findOneAndUpdate, one can see that before the update, the signature was as follows:
Query<T | null, EnforceDocument<T, TMethods>, T>. Note the explicit T | null as part of the Query return type.
Now, after the update, the same function on the Model has the signature QueryWithHelpers<EnforceDocument<T, TMethods, TVirtuals>, EnforceDocument<T, TMethods, TVirtuals>, TQueryHelpers, T> - Where null is not a possibility anymore, at least according to the types.

Note that the signature of Query has not changed in that regard, it still allows DocType | null - We simply restrict the type in the Model, which we probably shouldn't.