approx_red = len(approxPolyDP(self.red.contour, 0.01 * arcLength(self.red.contour, True), True))
    cv2.error: C:projectsopencv-pythonopencvmodulesimgprocsrcshapedescr.cpp:237: error: (-215) count >= 0 && (depth == 5 || depth == 4) in function cv::arcLength

try:
    approx_red = len(approxPolyDP(self.red.contour, 0.01 * arcLength(self.red.contour, True), True))
except cv2.error:
    approx_red = 0

OpenCV Error: Assertion failed (count >= 0 && (depth == 5 || depth == 4)) in cv::arcLength, file C:projectsopencv-pythonopencvmodulesimgprocsrcshapedescr.cpp, line 237
OpenCV Error: Assertion failed (count >= 0 && (depth == 5 || depth == 4)) in cv::arcLength, file C:projectsopencv-pythonopencvmodulesimgprocsrcshapedescr.cpp, line 237
OpenCV Error: Assertion failed (count >= 0 && (depth == 5 || depth == 4)) in cv::arcLength, file C:projectsopencv-pythonopencvmodulesimgprocsrcshapedescr.cpp, line 237
(...)