command-not-found works , however is showing that warning.
WARNING:root:could not open file ‘/etc/apt/sources.list’
Whonix does not ship
/etc/apt/sources.list but only files in
/etc/apt/sources.list.d/ drop-in folder.
( https://github.com/Whonix/anon-apt-sources-list )
That is because file
/etc/apt/sources.list managed by a package could conflict with local users, causing interactive dpkg config resolution dialog.
Considering to apply the following workaround.
sudo touch /etc/apt/sources.list sudo chmod o+r /etc/apt/sources.list
The latter command required due to umask hardening. (Change default umask.)
Any reason against creating an empty
/etc/apt/sources.list which is not managed by any package?
 Well, perhaps except from requriing another workaround which breaks it, see this post: Change default umask..