Concern about thermostat plug...

I have a 99 Solara SLE V6, and on the metal tubing that goes to the engine block/thermostat, there's a gray socket with nothing plugged into it. Do you guys know if something in my car is missing? Can someone check their 1MZ-FE and tell me? The plug is located on top of the bell housing to the thermostat. It's on the driver's side of the engine block.

here's a picture showing the bellhousing to the thermostat. (Maybe not technically a bellhousing)