Query creation using Projection & Unwind Operation

Working with Data Java Frameworks
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1

I am trying to create query using Projection & Unwind Operation to fetch necessary data which we want to process further.

ProjectionOperation initialProjection = Aggregation.project()
.and(“_id”).as(“_id”)
.and(“correlationId”).as(“correlationId”)
.and(“result.detections”).as(“detections”)

UnwindOperation unwindOpn = Aggregation.unwind(“result.detections”);

List postCriteriaList = new ArrayList<>();
postCriteriaList.add(new Criteria().andOperator(
Criteria.where(“result.detections.pictureName”).exists(true),
Criteria.where(“result.detections.pictureName”).ne(“”)
));

Criteria postMatchCriteria = new Criteria().andOperator(postCriteriaList);
MatchOperation postMatch = Aggregation.match(postMatchCriteria);

    Aggregation aggregation = Aggregation.newAggregation(
                preMatch, 
                unwindOpn, 
                projection, 
                postMatch)

AggregationResults<DetectionsUnwind> detectionsDataAggr = mongoTemplate.aggregate(aggregation, CASES_COLLECTION, DetectionsUnwind.class);

DetectionsUnwind class contains all the necessary fields which we want to display as output.

Now using this code we are getting error -

java.lang.IllegalArgumentException: Invalid reference 'result.detections'!
	at org.springframework.data.mongodb.core.aggregation.ExposedFieldsAggregationOperationContext.getReference(ExposedFieldsAggregationOperationContext.java:114)
	at org.springframework.data.mongodb.core.aggregation.ExposedFieldsAggregationOperationContext.getReference(ExposedFieldsAggregationOperationContext.java:77)
	at org.springframework.data.mongodb.core.aggregation.UnwindOperation.toDocument(UnwindOperation.java:95)
	at org.springframework.data.mongodb.core.aggregation.AggregationOperation.toPipelineStages(AggregationOperation.java:55)
	at org.springframework.data.mongodb.core.aggregation.AggregationOperationRenderer.toDocument(AggregationOperationRenderer.java:56)
	at org.springframework.data.mongodb.core.aggregation.AggregationPipeline.toDocuments(AggregationPipeline.java:81)
	at org.springframework.data.mongodb.core.aggregation.Aggregation.toPipeline(Aggregation.java:716)
	at org.springframework.data.mongodb.core.AggregationUtil.createPipeline(AggregationUtil.java:112)
	at org.springframework.data.mongodb.core.MongoTemplate.doAggregate(MongoTemplate.java:2165)
	at org.springframework.data.mongodb.core.MongoTemplate.doAggregate(MongoTemplate.java:2140)
	at org.springframework.data.mongodb.core.MongoTemplate.aggregate(MongoTemplate.java:2134)
	at org.springframework.data.mongodb.core.MongoTemplate.aggregate(MongoTemplate.java:2035)