DATAJPA-1024 - TupleConverter now guards against single-element tuples with null value.

We now also return a single-element tuple value as is if it's null as for some reason some persistence providers (*cough* Hibernate *cough*) will return a single-element, null value containing tuple (instead of null in the first place) for queries that didn't yield a result.

src/main/java/org/springframework/data/jpa/repository/query/AbstractJpaQuery.java

@@ -269,7 +269,7 @@ public abstract class AbstractJpaQuery implements RepositoryQuery {
 
 				Object value = tuple.get(elements.get(0));
 
-				if (type.isInstance(value)) {
+				if (type.isInstance(value) || value == null) {
 					return value;
 				}
 			}

src/test/java/org/springframework/data/jpa/repository/query/TupleConverterUnitTests.java

@@ -24,6 +24,7 @@ import java.util.Arrays;
 import javax.persistence.Tuple;
 import javax.persistence.TupleElement;
 
+import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.mockito.Mock;
@@ -49,6 +50,17 @@ public class TupleConverterUnitTests {
 	@Mock TupleElement<String> element;
 	@Mock ProjectionFactory factory;
 
+	ReturnedType type;
+
+	@Before
+	public void setUp() throws Exception {
+
+		RepositoryMetadata metadata = new DefaultRepositoryMetadata(SampleRepository.class);
+		QueryMethod method = new QueryMethod(SampleRepository.class.getMethod("someMethod"), metadata, factory);
+
+		this.type = method.getResultProcessor().getReturnedType();
+	}
+
 	/**
 	 * @see DATAJPA-984
 	 */
@@ -56,11 +68,6 @@ public class TupleConverterUnitTests {
 	@SuppressWarnings("unchecked")
 	public void returnsSingleTupleElementIfItMatchesExpectedType() throws Exception {
 
-		RepositoryMetadata metadata = new DefaultRepositoryMetadata(SampleRepository.class);
-		QueryMethod method = new QueryMethod(SampleRepository.class.getMethod("someMethod"), metadata, factory);
-		ReturnedType type = method.getResultProcessor().getReturnedType();
-
-		doReturn(element).when(tuple).get(0);
 		doReturn(Arrays.asList(element)).when(tuple).getElements();
 		doReturn("Foo").when(tuple).get(element);
 
@@ -69,6 +76,21 @@ public class TupleConverterUnitTests {
 		assertThat(converter.convert(tuple), is((Object) "Foo"));
 	}
 
+	/**
+	 * @see DATAJPA-1024
+	 */
+	@Test
+	@SuppressWarnings("unchecked")
+	public void returnsNullForSingleElementTupleWithNullValue() throws Exception {
+
+		doReturn(Arrays.asList(element)).when(tuple).getElements();
+		doReturn(null).when(tuple).get(element);
+
+		TupleConverter converter = new TupleConverter(type);
+
+		assertThat(converter.convert(tuple), is(nullValue()));
+	}
+
 	static interface SampleRepository extends CrudRepository<Object, Long> {
 		String someMethod();
 	}