Fixed Item Loader bug that was preventing values that evaluate to False from...

Fixed Item Loader bug that was preventing values that evaluate to False from being loaded. Patch contributed by Anibal Pacheco. Closes #174

scrapy/contrib/loader/__init__.py

@@ -29,7 +29,7 @@ class ItemLoader(object):
 
     def add_value(self, field_name, value, *processors, **kw):
         value = self.get_value(value, *processors, **kw)
-        if not value:
+        if value is None:
             return
         if not field_name:
             for k,v in value.iteritems():
@@ -39,7 +39,7 @@ class ItemLoader(object):
 
     def replace_value(self, field_name, value, *processors, **kw):
         value = self.get_value(value, *processors, **kw)
-        if not value:
+        if value is None:
             return
         if not field_name:
             for k,v in value.iteritems():

scrapy/tests/test_contrib_loader.py

@@ -68,6 +68,11 @@ class ItemLoaderTest(unittest.TestCase):
         il.add_value(None, u'Jim', lambda x: {'name': x})
         self.assertEqual(il.get_collected_values('name'), [u'Marta', u'Pepe', u'Jim'])
 
+    def test_add_zero(self):
+        il = NameItemLoader()
+        il.add_value('name', 0)
+        self.assertEqual(il.get_collected_values('name'), [0])
+
     def test_replace_value(self):
         il = TestItemLoader()
         il.replace_value('name', u'marta')