Add 'Map to Expression' to Replicate Preview

In SDR we have a feature to ‘Map to Expression’ but that is not available in Replicate Preview (as far as I can tell?). In my use case, I have an Oracle column that sometimes has a value chr(0) which is the equivalent to NULL. NULL is also a separate value.

In our Postgres target database there is no concept of chr(0), so I would be attempting to create a case statement to map NULL and chr(0) → NULL. But I don’t think I currently have the ability to do this in Replicate today?