GH-2301 - Assert not null on domain class.

Author: michael-simons

src/main/java/org/springframework/data/neo4j/core/Neo4jTemplate.java

@@ -310,7 +310,8 @@ public <T> List<T> saveAll(Iterable<T> instances) {
 		}
 
 		Class<T> domainClass = (Class<T>) TemplateSupport.findCommonElementType(entities);
-		Neo4jPersistentEntity entityMetaData = neo4jMappingContext.getPersistentEntity(domainClass);
+		Assert.notNull(domainClass, "Could not determine common domain class to save.");
+		Neo4jPersistentEntity<?> entityMetaData = neo4jMappingContext.getPersistentEntity(domainClass);
 		if (entityMetaData.isUsingInternalIds() || entityMetaData.hasVersionProperty()
 				|| entityMetaData.getDynamicLabelsProperty().isPresent()) {
 			log.debug("Saving entities using single statements.");

src/main/java/org/springframework/data/neo4j/core/ReactiveNeo4jTemplate.java

@@ -306,7 +306,8 @@ public <T> Flux<T> saveAll(Iterable<T> instances) {
 		}
 
 		Class<T> domainClass = (Class<T>) TemplateSupport.findCommonElementType(entities);
-		Neo4jPersistentEntity entityMetaData = neo4jMappingContext.getPersistentEntity(domainClass);
+		Assert.notNull(domainClass, "Could not determine common domain class to save.");
+		Neo4jPersistentEntity<?> entityMetaData = neo4jMappingContext.getPersistentEntity(domainClass);
 
 		if (entityMetaData.isUsingInternalIds() || entityMetaData.hasVersionProperty()
 				|| entityMetaData.getDynamicLabelsProperty().isPresent()) {

src/main/java/org/springframework/data/neo4j/core/TemplateSupport.java

@@ -42,6 +42,10 @@ final class TemplateSupport {
 	@Nullable
 	static Class<?> findCommonElementType(Iterable<?> collection) {
 
+		if (collection == null) {
+			return null;
+		}
+
 		List<Class<?>> allClasses = StreamSupport.stream(collection.spliterator(), true)
 				.filter(o -> o != null)
 				.map(Object::getClass).collect(Collectors.toList());

src/test/java/org/springframework/data/neo4j/core/TemplateSupportTest.java

@@ -18,6 +18,7 @@
 import static org.assertj.core.api.Assertions.assertThat;
 
 import java.util.Arrays;
+import java.util.Collections;
 
 import org.junit.jupiter.api.Test;
 
@@ -76,6 +77,20 @@ void shouldNotFailWithNull() {
 		assertThat(type).isNotNull().isEqualTo(A.class);
 	}
 
+	@Test
+	void shouldNotFailWithNullInput() {
+
+		Class<?> type = TemplateSupport.findCommonElementType(null);
+		assertThat(type).isNull();
+	}
+
+	@Test
+	void shouldNotFailWithEmptyInput() {
+
+		Class<?> type = TemplateSupport.findCommonElementType(Collections.emptyList());
+		assertThat(type).isNull();
+	}
+
 	@Test
 	void shouldFindCommonElementTypeOfHumongousCollection() {