sequence item 0: expected str instance, NoneType found.Liveness Face recognize

I'm learning about liveness Detection.I'm doing something like:

ap = argparse.ArgumentParser()
ap.add_argument("-m", "--model", type=str,help="C:/liveness-detection-opencv/liveness.model")
ap.add_argument("-l", "--le", type=str,help="C:/liveness-detection-opencv/le.pickle")
ap.add_argument("-d", "--detector", type=str,help="C:/liveness-detection-opencv/face_detector/")
ap.add_argument("-c", "--confidence", type=float, default=0.5,help="minimum probability to filter weak detections")
args = vars(ap.parse_args())
protoPath = os.path.sep.join([args["detector"], "deploy.prototxt.txt"])
modelPath = os.path.sep.join([args["detector"], "res10_300x300_ssd_iter_140000.caffemodel"])
net = cv2.dnn.readNetFromCaffe(protoPath, modelPath)
model = load_model(args["model"])
le = pickle.loads(open(args["le"], "rb").read())
vs = VideoStream(src=0).start()
time.sleep(2.0)
while True:
    frame = vs.read()
    frame = imutils.resize(frame, width=600)
(h, w) = frame.shape[:2]
    blob = cv2.dnn.blobFromImage(cv2.resize(frame, (300, 300)), 1.0,(300, 300), (104.0, 177.0, 123.0))
    net.setInput(blob)
    detections = net.forward()
    for i in range(0, detections.shape[2]):
        confidence = detections[0, 0, i, 2]
       if confidence > args["confidence"]:
        box = detections[0, 0, i, 3:7] * np.array([w, h, w, h])
        (startX, startY, endX, endY) = box.astype("int")
        startX = max(0, startX)
        startY = max(0, startY)
        endX = min(w, endX)
        endY = min(h, endY)
        face = frame[startY:endY, startX:endX]
        face = cv2.resize(face, (32, 32))
        face = face.astype("float") / 255.0
        face = img_to_array(face)
        face = np.expand_dims(face, axis=0)
        preds = model.predict(face)[0]
        j = np.argmax(preds)
        label = le.classes_[j]
        label = "{}: {:.4f}".format(label, preds[j])
        cv2.putText(frame, label, (startX, startY - 10),cv2.FONT_HERSHEY_SIMPLEX, 0.5, (0, 0, 255), 2)
        cv2.rectangle(frame, (startX, startY), (endX, endY),(0, 0, 255), 2)
cv2.imshow("Frame", frame)
key = cv2.waitKey(1) & 0xFF
if key == ord("q"):
    break
cv2.destroyAllWindows()
vs.stop()

But it get error like this: [My error][1] [1]: https://i.stack.imgur.com/4waUO.png

Please tell me how to fix this problem./\