diff --git a/src/linkahead/common/models.py b/src/linkahead/common/models.py
index 679a741896c060fd3e4435bdde5e586a79630a7a..aa68817511332ea570a3c2a40d400b21a2ed5658 100644
--- a/src/linkahead/common/models.py
+++ b/src/linkahead/common/models.py
@@ -3536,7 +3536,7 @@ class Container(list):
 
             for prop in container_item.get_properties():
                 prop_dt = prop.datatype
-                if is_reference(prop_dt):
+                if prop_dt is not None and is_reference(prop_dt):
                     # add only if it is a reference, not a simple property
                     # Step 1: look for prop.value
                     if prop.value is not None: