If there are only comments in the file it will still result in an error: "E: Unable to parse package file /etc/apt/preferences (1)". In my opinion apt should handle this file like an empty file in this case.
If there are only comments in the file it will still result in an error: "E: Unable to parse package file /etc/apt/ preferences (1)". In my opinion apt should handle this file like an empty file in this case.