DATACMNS-867 - ReflectionRepositoryInvoker now avoids ConversionService for Optional creation.

We now manually create Optional instances as the ConversionService converts single-argument collections into an optional with only that element.

src/main/java/org/springframework/data/repository/support/ReflectionRepositoryInvoker.java

@@ -253,16 +253,8 @@ class ReflectionRepositoryInvoker implements RepositoryInvoker {
 
 	@SuppressWarnings("unchecked")
 	private <T> Optional<T> returnAsOptional(Object source) {
-
-		if (Optional.class.isInstance(source)) {
-			return (Optional<T>) source;
-		}
-
-		if (source == null) {
-			return Optional.empty();
-		}
-
-		return conversionService.convert(QueryExecutionConverters.unwrap(source), Optional.class);
+		return (Optional<T>) (Optional.class.isInstance(source) ? source
+				: Optional.ofNullable(QueryExecutionConverters.unwrap(source)));
 	}
 
 	/**

src/test/java/org/springframework/data/repository/support/ReflectionRepositoryInvokerUnitTests.java

@@ -254,6 +254,22 @@ public class ReflectionRepositoryInvokerUnitTests {
 		assertThat(invokeFindOne).isPresent();
 	}
 
+	@Test // DATACMNS-867
+	public void wrapsSingleElementCollectionIntoOptional() throws Exception {
+
+		ManualCrudRepository mock = mock(ManualCrudRepository.class);
+		when(mock.findAll()).thenReturn(Arrays.asList(new Domain()));
+
+		Method method = ManualCrudRepository.class.getMethod("findAll");
+
+		Optional<Object> result = getInvokerFor(mock).invokeQueryMethod(method, new LinkedMultiValueMap<>(), Pageable.unpaged(),
+				Sort.unsorted());
+
+		assertThat(result).hasValueSatisfying(it -> {
+			assertThat(it).isInstanceOf(Collection.class);
+		});
+	}
+
 	private static RepositoryInvoker getInvokerFor(Object repository) {
 
 		RepositoryMetadata metadata = new DefaultRepositoryMetadata(repository.getClass().getInterfaces()[0]);