Call compare-versions in preinst with no version

Binary package hint: alsa-utils

In alsa-utils.preinst script dpkg is called:

        if dpkg --compare-versions $2 le 1.0.21-1ubuntu1; then
                update-rc.d -f alsa-utils remove
                rm -f /etc/init.d/alsa-utils
        fi

in install phase, but $2 is empty and a error is show in console:

Unpacking alsa-utils (from .../alsa-utils_1.0.22-0ubuntu4_amd64.deb) ...
dpkg: --compare-versions takes three arguments: <version> <relation> <version>

Type dpkg --help for help about installing and deinstalling packages [*];
Use `dselect' or `aptitude' for user-friendly package management;
Type dpkg -Dhelp for a list of dpkg debug flag values;
Type dpkg --force-help for a list of forcing options;
Type dpkg-deb --help for help about manipulating *.deb files;
Type dpkg --license for copyright license and lack of warranty (GNU GPL) [*].

Please test $2 before using it.