Convert Mobi to Epub and send to E-Reader causes 500 internal server error

[JamesGardiner]

Describe the bug/problem
After clicking the Convert Mobi to Epub and send to E-Reader button in the Send to E-Reader dropdown menu, a 500 internal server error is displayed with the following traceback:

Traceback (most recent call last):
File "/usr/local/lib/python3.8/dist-packages/flask/app.py", line 2073, in wsgi_app
response = self.full_dispatch_request()
File "/usr/local/lib/python3.8/dist-packages/flask/app.py", line 1518, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/usr/local/lib/python3.8/dist-packages/flask/app.py", line 1516, in full_dispatch_request
rv = self.dispatch_request()
File "/usr/local/lib/python3.8/dist-packages/flask/app.py", line 1502, in dispatch_request
return self.ensure_sync(self.view_functions[rule.endpoint])(**req.view_args)
File "/usr/local/lib/python3.8/dist-packages/flask_login/utils.py", line 303, in decorated_view
return current_app.ensure_sync(func)(*args, **kwargs)
File "/app/calibre-web/cps/web.py", line 113, in inner
return f(*args, **kwargs)
File "/app/calibre-web/cps/web.py", line 1196, in send_to_ereader
result = send_mail(book_id, book_format, convert, current_user.kindle_mail, config.config_calibre_dir,
File "/app/calibre-web/cps/helper.py", line 215, in send_mail
return convert_book_format(book_id, calibrepath, u'epub', book_format.lower(), user_id, ereader_mail)
File "/app/calibre-web/cps/helper.py", line 78, in convert_book_format
file_path = os.path.join(calibre_path, book.path, data.name)
AttributeError: 'NoneType' object has no attribute 'name'

To Reproduce
Steps to reproduce the behavior:

1. Go to the books view
2. Click on a book that you have an epub version of
3. Click Send to e-reader
4. Click Convert Mobi to Epub and send to E-Reader
5. See error

Logfile
Add content of calibre-web.log file or the relevant error, try to reproduce your problem with "debug" log-level to get more output.

Expected behavior
The books should be converted to mobi and send to the correct e-reader for the user

Environment (please complete the following information):

• Docker container: https://github.com/linuxserver/docker-calibre-web (nightly)
• Browser: Firefox 102.0.1