DATAJPA-23 - Fixed query building for IsNull and IsNotNull.

Use the actually accessed path instead of the root object. Added test cases to verify behaviour.

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

@@ -175,9 +175,9 @@ root.<Comparable> get(part.getProperty().toDotPath()),
             return builder.lessThan(getComparablePath(root, part),
                     nextAsComparable(iterator));
         case IS_NULL:
-            return root.isNull();
+            return path.isNull();
         case IS_NOT_NULL:
-            return root.isNotNull();
+            return path.isNotNull();
         case LIKE:
             return builder.like(root.<String> get(part.getProperty()
                     .toDotPath()), iterator.next().toString());

src/test/java/org/springframework/data/jpa/repository/UserRepositoryTests.java

@@ -759,6 +759,31 @@ public void executesFindByColleaguesLastnameCorrectly() throws Exception {
     }
 
 
+    @Test
+    public void executesFindByNotNullLastnameCorrectly() throws Exception {
+
+        flushTestUsers();
+        List<User> result = repository.findByLastnameNotNull();
+
+        assertThat(result.size(), is(3));
+        assertThat(result, hasItems(firstUser, secondUser, thirdUser));
+    }
+
+
+    @Test
+    public void executesFindByNullLastnameCorrectly() throws Exception {
+
+        flushTestUsers();
+        User forthUser =
+                repository.save(new User("Foo", null, "email@address.com"));
+
+        List<User> result = repository.findByLastnameNull();
+
+        assertThat(result.size(), is(1));
+        assertThat(result, hasItems(forthUser));
+    }
+
+
     private Page<User> executeSpecWithSort(Sort sort) {
 
         flushTestUsers();

src/test/java/org/springframework/data/jpa/repository/sample/UserRepository.java

@@ -190,4 +190,10 @@ List<User> findByFirstnameOrLastname(@Param("lastname") String lastname,
 
 
     List<User> findByColleaguesLastname(String lastname);
+
+
+    List<User> findByLastnameNotNull();
+
+
+    List<User> findByLastnameNull();
 }