GH-2301 - Assert not null on domain class and ensure a type could be determined.

Fixes #2301.

Author: michael-simons

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

@@ -431,7 +431,8 @@ private <T> List<T> saveAllImpl(Iterable<T> instances, @Nullable List<PropertyDe
 		}
 
 		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

@@ -448,7 +448,8 @@ private <T> Flux<T> saveAllImpl(Iterable<T> instances, @Nullable List<PropertyDe
 		}
 
 		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

@@ -66,6 +66,10 @@ enum FetchType {
 	@Nullable
 	public static Class<?> findCommonElementType(Iterable<?> collection) {
 
+		if (collection == null) {
+			return null;
+		}
+
 		Collection<Class<?>> allClasses = StreamSupport.stream(collection.spliterator(), true)
 				.filter(o -> o != null)
 				.map(Object::getClass).collect(Collectors.toSet());

src/main/java/org/springframework/data/neo4j/repository/query/Neo4jQuerySupport.java

@@ -185,18 +185,19 @@ final Object convertParameter(Object parameter, @Nullable Function<Object, Value
 			return convertBoundingBox((BoundingBox) parameter);
 		}
 
-		Class<?> type;
-		if (parameter instanceof Collection && mappingContext
-				.hasPersistentEntityFor(TemplateSupport.findCommonElementType((Collection) parameter))) {
-
-			EntityWriter<Object, Map<String, Object>> objectMapEntityWriter = Neo4jNestedMapEntityWriter
-					.forContext(mappingContext);
-
-			return ((Collection<?>) parameter).stream().map(v -> {
-				Map<String, Object> result = new HashMap<>();
-				objectMapEntityWriter.write(v, result);
-				return result;
-			}).collect(Collectors.toList());
+		if (parameter instanceof Collection) {
+			Class<?> type = TemplateSupport.findCommonElementType((Collection) parameter);
+			if (type != null && mappingContext.hasPersistentEntityFor(type)) {
+
+				EntityWriter<Object, Map<String, Object>> objectMapEntityWriter = Neo4jNestedMapEntityWriter
+						.forContext(mappingContext);
+
+				return ((Collection<?>) parameter).stream().map(v -> {
+					Map<String, Object> result = new HashMap<>();
+					objectMapEntityWriter.write(v, result);
+					return result;
+				}).collect(Collectors.toList());
+			}
 		}
 
 		if (mappingContext.hasPersistentEntityFor(parameter.getClass())) {

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() {
 

src/test/java/org/springframework/data/neo4j/integration/imperative/RepositoryIT.java

@@ -3101,6 +3101,14 @@ void findByIn(@Autowired PersonRepository repository) {
 			assertThat(persons).hasSize(1).contains(person2);
 		}
 
+		@Test // GH-2301
+		void findByEmptyIn(@Autowired PersonRepository repository) {
+
+			List<PersonWithAllConstructor> persons = repository
+					.findAllByFirstNameIn(Collections.emptyList());
+			assertThat(persons).isEmpty();
+		}
+
 		@Test
 		void findByNotIn(@Autowired PersonRepository repository) {