DATAMONGO-2153 - Fix domain type field mapping for change stream aggregations.

We now make sure to call the delegate AggregationOperationContext without potentially overriding arguments. Without this change potentially registered target types would be overridden with null.

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/NestedDelegatingExpressionAggregationOperationContext.java

@@ -43,6 +43,15 @@ class NestedDelegatingExpressionAggregationOperationContext implements Aggregati
 		this.delegate = referenceContext;
 	}
 
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.mongodb.core.aggregation.AggregationOperationContext#getMappedObject(org.bson.Document)
+	 */
+	@Override
+	public Document getMappedObject(Document document) {
+		return delegate.getMappedObject(document);
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.mongodb.core.aggregation.AggregationOperationContext#getMappedObject(org.bson.Document, java.lang.Class)

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/PrefixingDelegatingAggregationOperationContext.java

@@ -55,6 +55,15 @@ public class PrefixingDelegatingAggregationOperationContext implements Aggregati
 		this.blacklist = new HashSet<>(blacklist);
 	}
 
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.mongodb.core.aggregation.AggregationOperationContext#getMappedObject(org.bson.Document)
+	 */
+	@Override
+	public Document getMappedObject(Document document) {
+		return doPrefix(delegate.getMappedObject(document));
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.mongodb.core.aggregation.AggregationOperationContext#getMappedObject(org.bson.Document, java.lang.Class)