/usr/share/debbugs/templates/en_US/mail/invalid_user.tmpl is in debbugs-web 2.6.0.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | Your message tried to set a usertag, but didn't have a valid
user set ('{$user}' isn't valid)
|