Is it tested image corner detection of opencv?

[Godgang]

I'm not working on correctly saving detected_corners images
I think error in img_corners_est.py at line 61, 62

ret, corners = cv2.findChessboardCorners(img, size,
                                                 flags=cv2.CALIB_CB_ADAPTIVE_THRESH + cv2.CALIB_CB_NORMALIZE_IMAGE + cv2.CALIB_CB_FAST_CHECK)
 corners_reshaped=corners.reshape((size[1],size[0],2))

because corners type is nonetype, reshpae function could not work.

My thoughts may not be correct, but please reply.