Mystery: Missing Thermostat Sensor, loose, but capped electrical connector.

I was replacing fuel filter on my 2012 ML350 BlueTec, when I noticed that thermostat is missing temperature sensor on top (its black plastic electrical connector is seen on top of 365 picture, attached). Strange, but I also found loose, but capped electrical connector with wire harness length matching sensor location. Part number for thermostat is 6422001615 On part diagram I don't see separate part number for the sensor, not sure if sensor is shown on the drawing either. Car works fine, displays coolant temperature on dash, no OBD2 warnings or console messages, no SEL. I wonder if someone knows whether this sensor can be purchased separately. Is there a part# for it? Should it be installed on 2012 ml350 bluetec model? Last pic shows that it was installed on 2011 model. Air inlet and charge pipe look like on prev. gen of OM642 installed on W164). But part# is, I think, the same for W164 and W166.
Thank you for your expertise in this matter.

Pictures and copy of the above are also uploaded to : http://mbworld.org/forums/new-m-class-w166/589890-mystery-missing-thermostat-sensor-loose-but-capped-electrical-connector.html#ixzz3df8tEmY6