Why R is not considered in cv2.undistortPoints?

Why following pairs can get same result respectively? R is not considered in the function.

Pair One:
cv2.undistortPoints(pts, K, None,None, None)
cv2.undistortPoints(pts, K, None,R, None)

Pair Two:
cv2.undistortPoints(pts, K, D,None, None)
cv2.undistortPoints(pts, K, D, R, None)