TriggerEvent parameters from Activator in data pipeline

We have created an Activator that reacts to a csv file being created in a specific Lakehouse Files folder. This triggers a data pipeline in which we want to ingest this file into a Delta Lake table in the Lakehouse.

In the last section 'Setting expression values with the trigger file name and folder name' of the documentation Data pipelines storage event triggers in Data Factory - Microsoft Fabric | Microsoft Learn

, it states that TriggerEvent parameters can be used in the expression builder. Although I can see parameters like 'pipeline()?.TriggerEvent?.Subject', they always seem to be NULL when the pipeline is triggered through the activator!?