Why oerationType is null in ChangeStreamEvent(CosmosDB with Mongo Api)?

Hi I need to test change streams on Cosmos db. I have this code

private Flux<ChangeStreamEvent<T>> startChangeStream(DbChangeOffset offset) {
        List<String> operationTypeFilter = List.of("insert", "update", "replace");

        Aggregation aggregation = Aggregation.newAggregation(
                Aggregation.match(Criteria.where("operationType").in(operationTypeFilter)),
                Aggregation.project("_id", "fullDocument", "ns", "documentKey"));

        var optionsBuilder = ChangeStreamOptions.builder()
                .filter(aggregation)
                .fullDocumentLookup(FullDocument.UPDATE_LOOKUP);

        if (offset.getResumeToken() == null) {
            optionsBuilder.resumeAt(bsonTimestamp(offset));
        } else {
            optionsBuilder.startAfter(new BsonDocument().append("_data", new BsonString(offset.getResumeToken())));
        }

        return mongoTemplate.changeStream(collectionName, optionsBuilder.build(), collectionType)
                .doOnNext(event -> log.debug("Raw change stream event: {}", event.getRaw()))
                .doOnNext(event -> {
                    if (event.getRaw().getOperationType() == null) {
                        log.warn("Missing operationType in ChangeStreamEvent: {}", event);
                    } else {
                        log.debug("Processed ChangeStreamEvent with operationType={}", event.getRaw().getOperationType());
                    }
                })
                .doOnError(e -> log.error("Error in change stream for collection: {}", collectionName, e));
    }
```  But I am getting this error Missing operationType in ChangeStreamEvent: ChangeStreamEvent {raw=ChangeStreamDocument{ operationType=null, resumeToken={"_data": {"$binary":etc.. Does someon know why my operationType is null?