Fix aggregation projection.

Closes #5115
Original pull request: #5117

Author: christophstrobl

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

@@ -315,7 +315,7 @@ public <T> TypedOperations<T> forType(@Nullable Class<T> entityClass) {
 	public <M, D> EntityProjection<M, D> introspectProjection(Class<M> resultType, Class<D> entityType) {
 
 		MongoPersistentEntity<?> persistentEntity = queryMapper.getMappingContext().getPersistentEntity(entityType);
-		if (persistentEntity == null && !resultType.isInterface() || ClassUtils.isAssignable(Document.class, resultType)) {
+		if (persistentEntity == null && !resultType.isInterface() || ClassUtils.isAssignable(Map.class, resultType)) {
 			return (EntityProjection) EntityProjection.nonProjecting(resultType);
 		}
 		return introspector.introspect(resultType, entityType);

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/AggregationTests.java

@@ -36,6 +36,7 @@
 import java.util.Collections;
 import java.util.Date;
 import java.util.List;
+import java.util.Map;
 import java.util.Objects;
 import java.util.Optional;
 import java.util.Scanner;
@@ -2124,6 +2125,25 @@ void projectShouldResetContextToAvoidMappingFieldsAgainstANoLongerExistingTarget
 		assertThat(mappedResults.get(0)).containsEntry("itemId", "1");
 	}
 
+	@Test // GH-5115
+	@SuppressWarnings({ "rawtypes", "unchecked" })
+	void aggregationAllowsToReadBackRawDocumentAsMap() {
+
+		mongoTemplate.insert(List.of( //
+				Item.builder().itemId("1").build(), //
+				Item.builder().itemId("2").build(), //
+				Item.builder().itemId("3").build()), //
+				Item.class);
+
+		TypedAggregation<Item> aggregation = newAggregation(Item.class, count().as("count"));
+
+		AggregationResults<Map> result = mongoTemplate.aggregate(aggregation, Map.class);
+		Map<Object, Object> uniqueResult = result.getUniqueMappedResult();
+
+		assertThat(uniqueResult).containsKey("count") //
+				.extracting(it -> it.get("count")).isEqualTo(3);
+	}
+
 	private void createUsersWithReferencedPersons() {
 
 		mongoTemplate.dropCollection(User.class);