From c7800a65493be31f49d44ae89855242f35170d18 Mon Sep 17 00:00:00 2001
From: Christoph Strobl <christoph.strobl@broadcom.com>
Date: Tue, 30 Apr 2024 09:59:01 +0200
Subject: [PATCH] Fix NPE when rendering untyped aggregation operation as part
 of criteria query.

Resolves: #4687
Original pull request: #4695
---
 .../data/mongodb/core/convert/QueryMapper.java           | 7 +++++--
 .../data/mongodb/core/convert/QueryMapperUnitTests.java  | 9 +++++++++
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/QueryMapper.java b/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/QueryMapper.java
index 38a107cc7..eaa7b2cb7 100644
--- a/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/QueryMapper.java
+++ b/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/QueryMapper.java
@@ -588,8 +588,11 @@ public class QueryMapper {
 		}
 
 		if (source instanceof AggregationExpression age) {
-			return age
-					.toDocument(new RelaxedTypeBasedAggregationOperationContext(entity.getType(), this.mappingContext, this));
+
+			if(entity == null) {
+				return age.toDocument();
+			}
+			return age.toDocument(new RelaxedTypeBasedAggregationOperationContext(entity.getType(), this.mappingContext, this));
 		}
 
 		if (source instanceof MongoExpression exr) {
diff --git a/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/convert/QueryMapperUnitTests.java b/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/convert/QueryMapperUnitTests.java
index 0e5beac6f..018dff7c5 100755
--- a/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/convert/QueryMapperUnitTests.java
+++ b/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/convert/QueryMapperUnitTests.java
@@ -1529,6 +1529,15 @@ public class QueryMapperUnitTests {
 		assertThat(mappedObject).isEqualTo("{ $expr : { $expr : { $gt : [ '$foo', '$budget'] } } }");
 	}
 
+	@Test // GH-4687
+	void usageOfUntypedAggregationShouldRenderOperationsAsIs() {
+
+		Query query = query(expr(Expr.valueOf(ComparisonOperators.valueOf("field").greaterThan("budget"))));
+		org.bson.Document mappedObject = mapper.getMappedObject(query.getQueryObject(),
+			context.getPersistentEntity(Object.class));
+		assertThat(mappedObject).isEqualTo("{ $expr : { $expr : { $gt : [ '$field', '$budget'] } } }");
+	}
+
 	@Test // GH-2750
 	void usesMongoExpressionDocumentAsIsIfItIsNotAnAggregationExpression() {