Behavior breaking change deserializing property with null value

[pierre-gautier]

Using spring-data-mongodb 4.1.5, when deserializaing a property with null value in database to an instanciated collection, the collection was not set to null.

With version 4.2.0, the collection is set to null.

While I do understand the intention and tends to be aligned with it, it's still a breaking change that may have numerous impacts in production.

WDYT ?

[christophstrobl]

Thank you for reporting! Do you by any chance have a complete minimal sample (something that we can unzip or git clone, build, and deploy) that reproduces the problem? That would help us quite a bit triaging the issue.

[pierre-gautier]

I don't but I'll spend some time on it

[pierre-gautier]

Would it be enough if I told you that the difference happens in MappingMongoConverter#readProperties ?
In 4.1.5 on line 610 documentAccessor.hasValue(prop) returns false while it returns true in 4.2.0.
Digging down it seems the issue comes from BsonUtils#hasValue that has changed here.

[christophstrobl]

@pierre-gautier Thanks again for bringing this to our attention!
The current behaviour is the intended one, using the MongoDB Document as source of truth for collection initialization.
We'll add a couple of tests to the current test suite to verify the intended behaviour and extended the reference documentation to cover collection property initialization.

[pierre-gautier]

Thanks for your answer.
As I said before I'm actually quite OK with this philosophy.
But I need to confirm that you are aware about the fact that it is an important behavior change and upgrading from 4.1.5 to 4.2.0 will cause NPEs in most applications using initialized collections, are you OK with that ?

[mp911de]

We should have introduced this change much earlier as the change is more honest. You can always intercept values in a constructor or, if you use @Access(PROPERTY), then you can intercept collection null values in setters.

Alternatively, you can make use of lifecycle events to post-process the Document values that are null for a collection.