opencv 4.1.2 - TypeError: Expected Ptr<cv::UMat> for argument '%s'

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I have opencv 4.1.2 installed on pi3B+ with a picamera connected and I am trying to use cv2 to find contours in delta image frame; here's the traceback that I get if cv2.contourArea(c) < conf["min_area"]: TypeError: Expected Ptr<cv::umat> for argument '%s'

Here's the code snippet that throws the above Traceback:

#threshold delta image, dilate threshold image to fill in holes, then find contours on threshold image
    thresh = cv2.threshold(frameDelta, conf["delta_thresh"], 255, cv2.THRESH_BINARY)[1]
    thresh = cv2.dilate(thresh, None, iterations=2)
    cnts = cv2.findContours(thresh.copy(), cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)

# loop over contours
for c in cnts:
    #if contour is too small, ignore it
    **if cv2.contourArea(c) < conf["min_area"]:**
          continue

    # compute bounding box for contour, draw it on the frame and update text
    (x, y, w, h) = cv2.boundingRect(c)
    cv2.rectangle(frame, (x, y), (x + w, y + h), (0, 255, 0), 2)
    text = "Occupied"

Is it a bug in cv 4.1.2? I noticed a similar bug was fixed in version 3.4 (#15834). If yes, will the fix be merged in opencv 4.1.2?