Fix writing collections where first element is null

Closes #2215

Author: tamland

spring-data-jdbc/src/test/java/org/springframework/data/jdbc/repository/JdbcRepositoryCustomConversionIntegrationTests.java

@@ -21,6 +21,7 @@
 
 import java.math.BigDecimal;
 import java.sql.JDBCType;
+import java.util.ArrayList;
 import java.util.Date;
 import java.util.List;
 import java.util.Set;
@@ -182,6 +183,19 @@ void saveAndLoadListOfDirectionsAsArray() {
 		assertThat(reloaded).isEqualTo(saved);
 	}
 
+	@Test
+	@EnabledOnFeature(TestDatabaseFeatures.Feature.SUPPORTS_ARRAYS)
+	void saveAndLoadListOfNullAsArray() {
+		var list = new ArrayList<Direction>();
+		list.add(null);
+
+		EntityWithDirections saved = repositoryWithDirections.save(new EntityWithDirections(null, list));
+
+		EntityWithDirections reloaded = repositoryWithDirections.findById(saved.id).orElseThrow();
+
+		assertThat(reloaded).isEqualTo(saved);
+	}
+
 	interface EntityWithStringyBigDecimalRepository extends CrudRepository<EntityWithStringyBigDecimal, CustomId> {
 
 		@Query("SELECT * FROM ENTITY_WITH_STRINGY_BIG_DECIMAL WHERE DIRECTION IN (:types)")

spring-data-relational/src/main/java/org/springframework/data/relational/core/conversion/MappingRelationalConverter.java

@@ -809,16 +809,7 @@ private Object writeCollection(Iterable<?> value, TypeInformation<?> type) {
 			return mapped;
 		}
 
-		// if we succeeded converting the members of the collection, we actually ignore the fallback targetType since that
-		// was derived without considering custom conversions.
-		Class<?> targetType = type.getType();
-		if (!mapped.isEmpty()) {
-
-			Class<?> targetComponentType = mapped.get(0).getClass();
-			targetType = Array.newInstance(targetComponentType, 0).getClass();
-		}
-
-		Object converted = getConversionService().convert(mapped, targetType);
+		Object converted = getConversionService().convert(mapped, type.getType());
 
 		Assert.state(converted != null, "Converted must not be null");