Item rule syntax for change order when item catalog category is changed

Summary

Validation Condition !changed item catalog category results in error: Invalid arguments for function Changed. (EGO-2745209)

Content

Hi,

I am trying to figure out the proper definition to trigger a change order when the item catalog category is changed.
No matter what I try, the validation of the item catalog category results in error.

Below is what I am using:

Name: New Item Rule
Severity: Needs approval
Change Order Type: Category Change
Enforce the change order type: Yes

IF Expression: [Item].[Item Basic].[Item Class] == "Test"  
*Validation Condition: !changed(Catalog[Default].Category[null])  
User Message: Category changed and requires approval.