TypeError: 'NoneType' object is not subscriptable

[ WARN:0@1.299] global D:\a\opencv-python\opencv-python\opencv\modules\imgcodecs\src\loadsave.cpp (239) cv::findDecoder imread_('./datasets/mobile_data_img\'): can't open/read file: check file path/integrity
Traceback (most recent call last):
File "main.py", line 146, in
tf.app.run()
File "C:\Users\For36\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.7_qbz5n2kfra8p0\LocalCache\local-packages\Python37\site-packages\tensorflow\python\platform\app.py", line 125, in run
_sys.exit(main(argv))
File "main.py", line 114, in main
max_to_keep=FLAGS.max_to_keep)
File "C:\Users\For36\Desktop\New folder\DCGAN-tensorflow-master\model.py", line 93, in __init__
imreadImg = imread(self.data[0])
File "C:\Users\For36\Desktop\New folder\DCGAN-tensorflow-master\utils.py", line 56, in imread
img_rgb = img_bgr[..., ::-1]
TypeError: 'NoneType' object is not subscriptable

how do i fix this