What were you trying to do that didn't work?

As subject

Please provide the package NVR for which bug is seen:

libvirt v9.9.0-60-g3ad5817053

qemu-kvm-8.1.0-4.el9.x86_64

How reproducible:

100%

Steps to reproduce

1. Prepare a running VM
2. Attach a CDROM with empty source

Disk XML:

<disk type="file" device="cdrom">
  <driver name="qemu" type="raw"/>
  <target dev="sdc" bus="scsi" tray="open"/>
  <readonly/>
</disk>

~ virsh attach-device rhel-9.2 /tmp/sdc.xml
error: Failed to attach device from /tmp/sdc.xml
error: internal error: argument key 'filename' must not have null value

virtqemud log: virtqemud.log

Expected results

Success to attach a CDROM without source

Actual results

As above