500 Internal Server Error - on directory/file that does not exist, instead of 404

[clach04]

http://localhost:9999/file/does_not_exist

results in:

Internal Server Error

The server encountered an internal error and was unable to complete your request. Either the server is overloaded or there is an error in the application.

500, instead of 404.

   File "...webook_server/webook_opds_server.py", line 833, in opds_browse
     files = os.listdir(os_path)
 FileNotFoundError: [Errno 2] No such file or directory: '...../does_not_exist'