Resetting `default_kernel` using `qubes-prefs` gives confusing results

[RandyTheOtter]

How to file a helpful issue

Qubes OS release

4.3

Brief summary

Resetting default_kernel using qubes-prefs returns Failed to access 'default_kernel' property error and unsets default_kernel. This is confusing because qubes-prefs has no real issues accessing properties, the error is caused by default_kernel property not having a default by design.

Steps to reproduce

qubes-prefs -D default_kernel

Expected behavior

Not knowing that default_kernel has no default, I would expect it to reset value to the latest stable kernel.

With the lack of default default in mind, keeping default_kernel value untouched feels like a right step. Returning a better error message is also good.

In both cases I'm not sure how reasonable it is to change qubes-prefs just for this one edge case. Perhaps improving documentation around this might be better overall.

Actual behavior

$ qubes-prefs -D default_kernel
qubes-prefs: error: Failed to access 'default_kernel' property
$ qubes-prefs default_kernel

$

Additional information