spring-projectsGH-2544 Neo4jTemplate.saveAllAs returns emptyList when given empty iterable.

Author: cberes

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

@@ -99,6 +99,7 @@
  * @author Michael J. Simons
  * @author Philipp Tölle
  * @author Gerrit Meier
+ * @author Corey Beres
  * @soundtrack Motörhead - We Are Motörhead
  * @since 6.0
  */
@@ -520,6 +521,10 @@ public <T, R> List<R> saveAllAs(Iterable<T> instances, Class<R> resultType) {
 
 		Assert.notNull(resultType, "ResultType must not be null!");
 
+		if (!instances.iterator().hasNext()) {
+			return Collections.emptyList();
+		}
+
 		Class<?> commonElementType = TemplateSupport.findCommonElementType(instances);
 
 		if (resultType.isAssignableFrom(commonElementType)) {

src/test/java/org/springframework/data/neo4j/integration/imperative/Neo4jTemplateIT.java

@@ -76,6 +76,7 @@
  * @author Gerrit Meier
  * @author Michael J. Simons
  * @author Rosetta Roberts
+ * @author Corey Beres
  */
 @Neo4jIntegrationTest
 class Neo4jTemplateIT {
@@ -795,6 +796,13 @@ void saveAllAsWithClosedProjectionShouldWork() {
 		assertThat(people).allMatch(p -> p.getAddress() != null);
 	}
 
+	@Test // GH-2544
+	void saveAllAsWithEmptyList() {
+		List<ClosedProjection> projections = neo4jTemplate.saveAllAs(Collections.emptyList(), ClosedProjection.class);
+
+		assertThat(projections).isEmpty();
+	}
+
 	@Test
 	void updatingFindShouldWork() {
 		Map<String, Object> params = new HashMap<>();