handling code. In particular, if you had a section of XML like:
<disk type='file' device='cdrom'>
<target dev='hdc' bus='ide'/>
<readonly/>
</disk>
This used to work with older libvirt, but now fails. This is because we are
actually passing the literal string (null) to the qemu command-line, which qemu
barfs on. This patch fixes it up by making it blank, which allows qemu to
continue on it's merry way.
Signed-off-by: Chris Lalancette <clalance@redhat.com>
