removed commented code and add test for error handling

scrapy/loader/__init__.py

@@ -115,9 +115,6 @@ class ItemLoader(object):
             if value is not None:
                 item[field_name] = value
 
-        # for loader in self._subloaders:
-        #     loader.load_item()
-
         return item
 
     def get_output_value(self, field_name):

tests/test_loader.py

@@ -707,6 +707,11 @@ class SubselectorLoaderTest(unittest.TestCase):
         self.assertEqual(item['url'], [u'http://www.scrapy.org'])
         self.assertEqual(item['image'], [u'/images/logo.png'])
 
+    def test_nested_bad_arguments(self):
+        l = NestedItemLoader(response=self.response)
+        with self.assertRaises(ValueError):
+            l.nested_loader(css="#id", xpath="//footer")
+
 
 class SelectJmesTestCase(unittest.TestCase):
         test_list_equals = {