--- a/app/soc/modules/ghop/models/task.py	Sun Nov 08 12:11:14 2009 -0800
+++ b/app/soc/modules/ghop/models/task.py	Tue Nov 10 13:59:15 2009 +0100
@@ -43,10 +43,7 @@
   """Model for storing all Task tags.
   """
 
-  #: Each task_type tag is scoped under the program. 
-  scope = db.ReferenceProperty(reference_class=soc.models.linkable.Linkable,
-                               required=True,
-                               collection_name='task_type_tags')
+  #: Each task_type tag is scoped under the program.
 
   order = db.IntegerProperty(required=True, default=0)
 
@@ -147,6 +144,10 @@
   def get_or_create(cls, scope, tag_name, order=0):
     """Get the Tag object that has the tag value given by tag_value.
     """
+
+    if not scope:
+      return None
+
     tag_key_name = cls.__key_name(scope.key().name(), tag_name)
     existing_tag = cls.get_by_key_name(tag_key_name)
     if existing_tag is None:

--- a/app/taggable/taggable.py	Sun Nov 08 12:11:14 2009 -0800
+++ b/app/taggable/taggable.py	Tue Nov 10 13:59:15 2009 +0100
@@ -1,5 +1,7 @@
 from google.appengine.ext import db
+
 import string
+import soc.models.linkable
     
 class Tag(db.Model):
   "Google AppEngine model for store of tags."
@@ -19,6 +21,11 @@
   auto_delete = db.BooleanProperty(required=True, default=False)
   "If true, a tag instance should be deleted when tagged_count reaches zero."
 
+  scope = db.ReferenceProperty(reference_class=soc.models.linkable.Linkable,
+                               required=False,
+                               collection_name='task_type_tags')
+  "Each tag is scoped under some linkable model."
+
   @classmethod
   def __key_name(cls, tag_name):
     return cls.__name__ + '_' + tag_name