GH-2124 - Fix failing save for uninitialized maps of dynamic properties.

This closes #2124.

Author: michael-simons

src/main/java/org/springframework/data/neo4j/core/mapping/MappingSupport.java

@@ -46,7 +46,12 @@ public final class MappingSupport {
 	 * @return A unified collection (Either a collection of Map.Entry for dynamic and relationships with properties or a
 	 *         list of related values)
 	 */
-	public static @Nullable Collection<?> unifyRelationshipValue(Neo4jPersistentProperty property, Object rawValue) {
+	public static Collection<?> unifyRelationshipValue(Neo4jPersistentProperty property, @Nullable Object rawValue) {
+
+		if (rawValue == null) {
+			return Collections.emptyList();
+		}
+
 		Collection<?> unifiedValue;
 		if (property.isDynamicAssociation()) {
 			if (property.isDynamicOneToManyAssociation()) {

src/test/java/org/springframework/data/neo4j/integration/properties/DomainClasses.java

@@ -19,6 +19,7 @@
 import lombok.Getter;
 import lombok.Setter;
 
+import java.util.ArrayList;
 import java.util.Date;
 import java.util.HashMap;
 import java.util.List;
@@ -145,4 +146,32 @@ static class WeirdSource {
 		@Relationship(type = "ITS_COMPLICATED")
 		IrrelevantTargetContainer irrelevantTargetContainer;
 	}
+
+	@Node
+	@Getter @Setter
+	static class LonelySourceContainer {
+		@Id @GeneratedValue
+		private Long id;
+
+		@Relationship(type = "RELATIONSHIP_PROPERTY_CONTAINER")
+		RelationshipPropertyContainer single;
+
+		@Relationship(type = "RELATIONSHIP_PROPERTY_CONTAINER_2")
+		List<RelationshipPropertyContainer> multiNull;
+
+		@Relationship(type = "RELATIONSHIP_PROPERTY_CONTAINER_3")
+		List<RelationshipPropertyContainer> multiEmpty = new ArrayList<>();
+
+		@Relationship
+		Map<String, List<IrrelevantTargetContainer>> dynNullList;
+
+		@Relationship
+		Map<String, List<SimpleGeneratedIDPropertyContainer>> dynEmptyList = new HashMap<>();
+
+		@Relationship
+		Map<String, SimpleGeneratedIDPropertyContainerWithVersion> dynNullSingle;
+
+		@Relationship
+		Map<String, SimplePropertyContainer> dynEmptySingle = new HashMap<>();
+	}
 }

src/test/java/org/springframework/data/neo4j/integration/properties/PropertyIT.java

@@ -235,6 +235,16 @@ void customConvertersForRelsMustBeTakenIntoAccount() {
 		}
 	}
 
+	@Test // GH-2124
+	void shouldNotFailWithEmptyOrNullRelationshipProperties() {
+
+		DomainClasses.LonelySourceContainer s = template.save(new DomainClasses.LonelySourceContainer());
+		try (Session session = driver.session()) {
+			long cnt = session.run("MATCH (m) WHERE id(m) = $id RETURN count(m)", Collections.singletonMap("id", s.getId())).single().get(0).asLong();
+			assertThat(cnt).isEqualTo(1L);
+		}
+	}
+
 	@Configuration
 	@EnableTransactionManagement
 	static class Config extends AbstractNeo4jConfig {

src/test/java/org/springframework/data/neo4j/integration/properties/ReactivePropertyIT.java

@@ -253,6 +253,22 @@ void customConvertersForRelsMustBeTakenIntoAccount() {
 		}
 	}
 
+	@Test // GH-2124
+	void shouldNotFailWithEmptyOrNullRelationshipProperties() {
+
+		List<Long> recorded = new ArrayList<>();
+		template.save(new DomainClasses.LonelySourceContainer())
+				.map(DomainClasses.LonelySourceContainer::getId)
+				.as(StepVerifier::create)
+				.recordWith(() -> recorded)
+				.expectNextCount(1L)
+				.verifyComplete();
+		try (Session session = driver.session()) {
+			long cnt = session.run("MATCH (m) WHERE id(m) = $id RETURN count(m)", Collections.singletonMap("id", recorded.get(0))).single().get(0).asLong();
+			assertThat(cnt).isEqualTo(1L);
+		}
+	}
+
 	@Configuration
 	@EnableTransactionManagement
 	static class Config extends AbstractReactiveNeo4jConfig {