python　画像処理でエラーが出ます。直し方を教えてください。

import os
import cv2
import glob



def resize_rectangle_img(from_dir,to_dir,size=None):
    #file_type = 'jpg'
    #img_list = glob.glob('./' + from_dir + '/*.' + file_type)
    files = os.listdir(from_dir)
    i = 0
    for file in files:

        img = cv2.imread(from_dir+file,1)
        #img.show()

        # Get the height and width of the loaded image
        height= img.shape[0]
        width = img.shape[1]
        x1 = y1 = 0
        x2 = width
        y2 = height
        diff = abs(height - width)
        if height > width:
            y1 = int(diff/2)
            y2 = height - y1
        elif width>height:
            x1 = int(diff/2)
            x2 = width - x1
        img = img[y1:y2,x1:x2]

        if size!=None:
            img = cv2.resize(img,(size,size))

        cv2.imwrite(to_dir+file,img)
        print(str(i))
        print("\n")
        i = i+1

if __name__ == '__main__':
    resize_rectangle_img('images/original/','images/resized/')
    print("=====Resized!=====")

File "resize.py", line 18, in resize_rectangle_img
    height= img.shape[0]
AttributeError: 'NoneType' object has no attribute 'shape'