==============
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/dist-packages/PIL/Image.py", line 2192, in save
    format = EXTENSION[ext]
KeyError: ''

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/mnt/run_drive/waifu2x/waifu2x-chainer/waifu2x.py", line 218, in <module>
    main()
  File "/mnt/run_drive/waifu2x/waifu2x-chainer/waifu2x.py", line 215, in main
    icc_profile=icc_profile)
  File "/usr/local/lib/python3.7/dist-packages/PIL/Image.py", line 2194, in save
    raise ValueError(f"unknown file extension: {ext}") f