WIP migrate attribute management to partial editing with 4 new features! See #1222.

New features include:

 - New clarity between null and empty string attributes
 - Attribute editing now shows appropriate UI widgets depending on data type
 - Attribute editing for enumerations now show a dropdown
 - Attribute editing is now schema sensitive

src/ifcblenderexport/blenderbim/bim/module/root/data.py

@@ -13,5 +13,5 @@ class Data:
         cls.products[product_id] = {
             "type": product.is_a(),
             "PredefinedType": product.PredefinedType if hasattr(product, "PredefinedType") else None,
-            "ObjectType": product.ObjectType or None
+            "ObjectType": product.ObjectType if hasattr(product, "ObjectType") else None
         }