如何清除Nonetype错误？

Question

好吧，因此，我试图制作一个带视频的小型压缩器，将其转换为帧，压缩每个帧，然后将压缩的帧组合回视频形式，而即时消息出现的错误是压缩帧与视频的组合。我无法解决。.请帮助

import cv2
import numpy as np
import os
import shutil
from os.path import isfile, join

def imgtovideo():
    pathIn= 'C:\\Users\\Dell\\Desktop\\dangol\\compressed'
    pathOut = 'C:\\Users\\Dell\\Desktop\\dangol\\video.avi'
    fps = 29.970
    frame_array = []
    files = [f for f in os.listdir(pathIn) if isfile(join(pathIn, f))]
    #for sorting the file names properly
    files.sort(key = lambda x: x[5:-4])
    files.sort()
    frame_array = []
    files = [f for f in os.listdir(pathIn) if isfile(join(pathIn, f))]
    #for sorting the file names properly
    files.sort(key = lambda x: x[5:-4])
    for i in range(len(files)):
        filename=pathIn + files[i]
        #reading each files
        img = cv2.imread(filename)
        height, width, layers = img.shape
        size = (width,height)

        #inserting the frames into an image array
        frame_array.append(img)
    out = cv2.VideoWriter(pathOut,cv2.VideoWriter_fourcc(*'DIVX'), fps, size)
    for i in range(len(frame_array)):
        # writing to a image array
        out.write(frame_array[i])
    out.release()
    os.chdir('../')
    shutil.rmtree('C:\\Users\\Dell\\Desktop\\dangol\\compressed')


if __name__ == "__imgtovideo__":
    imgtovideo()

Exception in Tkinter callback
Traceback (most recent call last):
  File "C:\Program Files\Python37\lib\tkinter\__init__.py", line 1705, in __call__
    return self.func(*args)
  File "C:\Users\Dell\Desktop\dangol\img_video.py", line 23, in imgtovideo
    height, width, layers = img.shape
AttributeError: 'NoneType' object has no attribute 'shape'