BREAKING CHANGE: apply minimize by default when updating document

[vkarpov15]

Fix #13782

Summary

This change is small code-wise, but significant and worth thinking about carefully. The docs on minimize say that Mongoose will, by default, "minimize" schemas by removing empty objects. but don't specify exactly when minimize is applied.

Right now, Mongoose only applies minimize() when $toObject() is called. So that means when you save() a new doc, Mongoose applies minimize() unless you set minimize: false option in your schema. However, if you try to update an existing doc's nested or subdocument property, Mongoose will currently not apply minimize: Mongoose will store an empty object in MongoDB. However, if you update a document array on an existing document, Mongoose will minimize the document array.

This behavior is inconsistent. This PR makes it so that Mongoose applies minimize() when updating an existing document with save(). However, I'm a bit worried about changing this behavior; I'm worried of unforeseen consequences. Any thoughts @hasezoey @AbdelrahmanHafez ?

Examples

[hasezoey]

Looks and sounds good to me, as long as all the tests still pass and this change is mentioned in the changelog, hopefully this wont turn into another strictQuery thing

[vkarpov15]

Yeah, the strictQuery issue is exactly what I'm worried about with this PR. I'll think a little more about it, but I think in the interest of learning our lessons from strictQuery, we shouldn't hesitate to remove this behavior if it causes strictQuery-like problems.