A bug of opencv4.1.0?

edit

I see the ChangeLog about opencv4.1 about new function calcOpticalFlowSparseRLOF. So I give a try:

Mat pre = imread("C:/Users/Lenovo/Desktop/33.png", 0);
Mat next = imread("C:/Users/Lenovo/Desktop/44.png", 0);
resize(next, next, pre.size());
vector<Point2f> points[2];

goodFeaturesToTrack(pre, points[0], 20, 0.01, 5);

vector<uchar> status;
Mat err;
calcOpticalFlowSparseRLOF(pre, next, points[0], points[1], status, err);

This is my two images:

pre:

next:

But whatever I run the code how much time, I cannot get nothing. Is it a bug or I missed something?