Using POJO serialization, updates seem to be problematic. Considering this POJO:

 
	@BsonId
	public String key;
	@BsonProperty("value")
	public ObjectNode value;  

Note, the "value" is Jackson.

To support this, it was registered a custom Codec for ObjectNode. Updates will not invoke the codec. For example:

 
	Document setters = new Document("value", Mappers.getJacksonMapper().createObjectNode());
	Document d = new Document("$set", setters);
	// does not invoke codec, you get []
	pojoCollection.updateOne(new Document("_id", "key1"), d);

The ObjectNode is replaced with [] in the resulting BSON, which makes subsequent POJO reads fail.

After some investigation, it was identified the root cause is [this line](https://github.com/mongodb/mongo-java-driver/blob/r3.12.5/bson/src/main/org/bson/codecs/DocumentCodec.java#L192) in the DocumentCodec. [This line](https://github.com/mongodb/mongo-java-driver/blob/r3.12.5/bson/src/main/org/bson/codecs/DocumentCodec.java#L192) special-cases encoding instances of Iterable with its own encoder. Normally this is not an issue. However in this case it is an issue because ObjectNode extends JsonNode which implements Iterable<JsonNode>. This prevents the process from falling through to [this line](https://github.com/mongodb/mongo-java-driver/blob/r3.12.5/bson/src/main/org/bson/codecs/DocumentCodec.java#L197).

As a workaround, the ObjectNode can be wrapped in some other class that does not implement Iterable, and provide a codec for that class as well.