python报错cannot unpack non-iterable NoneType object，求解决

在用opencv做图像识别的过程中报错，一共10个相同物体，只能识别出6个，且count为0

for pos in posList:
    angle = recRota(imgDilate, pos[0], pos[1], pos[0], pos[1], w, h, 0, draw=False)
    rota_params = cv2.getRotationMatrix2D(angle[0], angle=0, scale=1)
    rota_img = cv2.warpAffine(imgDilate, rota_params, (img_w, img_h))
    imgCrop = rota_img[pos[1]:pos[1] + h, pos[0]:pos[0] + w]
    #cv2.imshow('imgCrop', imgCrop)
    count = cv2.countNonZero(imgCrop)

识别出的imgCrop为

未识别出的imgCrop则报错

求各位大神指教