During the book downloading stage, a 500 error occurred

[GXY1122]

Calibre-Web
500 Internal Server Error
The server encountered an internal error and was unable to complete your request. There is an error in the application.
Traceback (most recent call last):
File "/lsiopy/lib/python3.12/site-packages/flask/app.py", line 1473, in wsgi_app
response = self.full_dispatch_request()
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/lsiopy/lib/python3.12/site-packages/flask/app.py", line 882, in full_dispatch_request
rv = self.handle_user_exception(e)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/lsiopy/lib/python3.12/site-packages/flask/app.py", line 880, in full_dispatch_request
rv = self.dispatch_request()
^^^^^^^^^^^^^^^^^^^^^^^
File "/lsiopy/lib/python3.12/site-packages/flask/app.py", line 865, in dispatch_request
return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args) # type: ignore[no-any-return]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/app/calibre-web/cps/usermanagement.py", line 97, in decorated_view
return login_required(func)(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/app/calibre-web/cps/cw_login/utils.py", line 296, in decorated_view
return current_app.ensure_sync(func)(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/app/calibre-web/cps/web.py", line 132, in inner
return f(*args, **kwargs)
^^^^^^^^^^^^^^^^^^
File "/app/calibre-web/cps/web.py", line 1248, in download_link
return get_download_link(book_id, book_format, client)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/app/calibre-web/cps/helper.py", line 1112, in get_download_link
return do_download_file(book, book_format, client, data1, headers)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/app/calibre-web/cps/helper.py", line 973, in do_download_file
response = make_response(send_from_directory(filename, download_name + "." + book_format))

TypeError: unsupported operand type(s) for +: 'NoneType' and 'str'

[OzzieIsaacs]

Without any context it makes no sense for me to do something with this issue

[sginestrini]

In my case, by looking at the full log, the problem was the populated field in 'External binaries' -> 'Path to Calibre Binaries' with a folder where no "Calibre" folder was present and this generate the error.