How to pass empty kernel to cv2.morphologyEx

In opencv java, I can use org.opencv.imgproc.Imgproc.morphologyEx(mat, mat, org.opencv.imgproc.Imgproc.MORPH_CLOSE, new org.opencv.core.Mat()); to deal with an image and get clear output image (just the main). Now I want to do the same stuff in opencv python: cv2.morphologyEx(img, cv2.MORPH_CLOSE, ??). I do not know what should be passed to ??. Any help?

just pass None