prevent failure when property is None

git-svn-id: https://svn.erp5.org/repos/public/erp5/sandbox/amount_generator@36903 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/Document/CategoryMovementGroup.py

@@ -43,7 +43,7 @@ class CategoryMovementGroup(PropertyMovementGroup):
     getProperty = getattr(movement, 'getMappedProperty', movement.getProperty)
     for prop in self.getTestedPropertyList():
       list_prop = '%s_list' % prop
-      property_dict[list_prop] = sorted(getProperty(list_prop))
+      property_dict[list_prop] = sorted(getProperty(list_prop) or ())
     return property_dict
 
   def test(self, document, property_dict, property_list=None, **kw):