Dear Maintainer,
Looks like xflock4 is missing a man page.
$ man xflock4
No manual entry for xflock4
See 'man 7 undocumented' for help when manual pages are not available.
$ dpkg -L xfce4-session|grep /usr/bin
/usr/bin
/usr/bin/xfce4-session-logout
/usr/bin/xfce4-session
/usr/bin/xflock4
/usr/bin/xfce4-session-settings
/usr/bin/startxfce4
$ dpkg -L xfce4-session|grep man
/usr/share/man
/usr/share/man/man1
/usr/share/man/man1/xfce4-session-settings.1.gz
/usr/share/man/man1/xfce4-session-logout.1.gz
/usr/share/man/man1/xfce4-session.1.gz
/usr/share/man/man1/startxfce4.1.gz