TypeError: object of type 'NoneType' has no len()

Hi, please help me
i use im2rec.py
so when i do so
python Downloads/im2rec.py Downloads/test . --center-crop --resize 224 --pack-label

i get the error

opencv@opencv-virtual-machine:~$ python Downloads/im2rec.py Downloads/test . --center-crop --resize 224 --pack-label
Creating .rec file from /home/opencv/Downloads/test/dog.lst in /home/opencv/Downloads/test
multiprocessing not available, fall back to single threaded encoding
imread read blank (None) image for file: /home/opencv/./data/img/h_87.jpg
Traceback (most recent call last):
File “Downloads/im2rec.py”, line 386, in
record.write_idx(item[0], s)
File “/home/opencv/.local/lib/python2.7/site-packages/mxnet/recordio.py”, line 285, in write_idx
File “/home/opencv/.local/lib/python2.7/site-packages/mxnet/recordio.py”, line 135, in write
TypeError: object of type ‘NoneType’ has no len()

What does it mean
here 87.jpg

i found the source of error, i forgot create data folder in root catalog

Thanks for providing your solution @Data_Miner