Merge branch 'dev' into f-191-fix-mypy-errors-in-models-py-and-complete-type-hints

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: