Petrucci Doubler Automation

So, in Stuido One 5 it seems like I can assign automation to manipulate any knob or effect in the Petrucci plugin, except toggling the doubler on and off.

Is this by design? Or am I just missing something. The doubler doesn’t seem like its an assignable option at all. It doesn’t even show up in the list of assignable functions.

Thank you.