Sludge in oil filler neck 2007 2.0d

Hi I’ve recently noticed that theres a white sludge in my oil filler neck that wasn’t there when i last did my oil change in November, just after a bit of advice really I’ve read that some models can get moisture build up and its nothing to really worry about but with this also being one of the tell tale signs of a blown head gasket i wanted to be sure before i cause damage. Theres no missing coolant and no white smoke, the car runs fine i do only short journeys 3 miles twice a day but i try to do at-least one 20 mile drive to clean the egr out each month.