2004 T6 Plug in engine What is it, whats missing??? See picture

Inside the engine compartment of a 2004 XC90 T6 there is a plug on the drivers side with nothing attached to it. What is it? And is there something supposed to be attached there? See pictures...

2004volvoengine connector circled.jpg
I have the same vehicle, and same connector not plugged in. I was wondering the same thing.