Description of problem: Running rawhide on aarch64/hikey I am trying to add additional hardware to a kvm guest.  When "Add Hardware" is clicked from the GUI, it displays "Error launching hardware dialog: 'NoneType' object is not iterable.



Version-Release number of selected component (if applicable): virt-manager-1.4.3-1.fc28.noarch

How reproducible: So far 100%, I tried it while running, stopped, and from a new instance.


Steps to Reproduce:
1. Install virt-manager/qemu/libvirt
2. run virt-manager, create new vm
3. From lightbulb/hardware config clikc "Add hardware"

Actual results:
Error launching hardware dialog: 'NoneType' object is not iterable

Traceback (most recent call last):
  File "/usr/share/virt-manager/virtManager/details.py", line 1407, in add_hardware
    self.addhw = vmmAddHardware(self.vm, self.is_customize_dialog)
  File "/usr/share/virt-manager/virtManager/addhardware.py", line 120, in __init__
    self._set_initial_state()
  File "/usr/share/virt-manager/virtManager/addhardware.py", line 320, in _set_initial_state
    self._build_panic_models(combo)
  File "/usr/share/virt-manager/virtManager/addhardware.py", line 980, in _build_panic_models
    for m in
virtinst.VirtualPanicDevice.get_models(self.vm.get_xmlobj().os):
TypeError: 'NoneType' object is not iterable


Expected results:
I can add additional hd's/etc.