Error when not specifying -o

[marcoduering]

Hi,
In version 2.0.1., I get an error when not specifying the output via -o, which was possible in version 1 and should still be possible in the current version, if I understand the documentation correctly. Is this a problem with my setup or perhaps a small bug? Everything works correctly when adding -o example.nii.gz.

Traceback (most recent call last):
  File "/usr/local/bin/hd-bet", line 8, in <module>
    sys.exit(main())
             ^^^^^^
  File "/opt/HD-BET/HD_BET/entry_point.py", line 53, in main
    hdbet_predict(args.input,args.output, predictor, keep_brain_mask=args.save_bet_mask,
  File "/opt/HD-BET/HD_BET/hd_bet_prediction.py", line 62, in hdbet_predict
    assert not isdir(output_file_or_folder), 'If input is a single file then output must be a filename, not a directory'
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<frozen genericpath>", line 42, in isdir
TypeError: stat: path should be string, bytes, os.PathLike or integer, not NoneType