Not sure that's an oil filter. I can't tell what kind of plastic it is from just the picture but it's pretty shiny, meaning it's a softer material.
My knee-jerk reaction is that it's a rock-catcher pre-filter for the air filtering system. Maybe it slides into a slot in the airbox?
EDIT: Turns out it was part of the lubrication system. It's called an "Oil filter screen", Kawasaki 490657004. Tough to tell from the parts diagram, but it looks like it covers the oil pump inlet and might stand vertically on the short end. The engine appears to have a regular filter as well (at least on the one I looked up).