Description of problem:

When commenting out the root file system entry in /etc/fstab, booting the DVD in Troubleshooting Mode crashes at OS detection:
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
1) Continue
2) Read-only mount
3) Skip to shell
4) Quit (Reboot)

Please make a selection from the above: 1

File "/usr/lib/python3.6/site-packages/dasbus/client/handler.py", line 419, in _call_method
_call_method
parameters = get_variant(in_type, parameters)
File "/usr/lib/python3.6/site-packages/dasbus/typing.py", line 124, in get_variant
return Variant(type_string, value)
File "/usr/lib64/python3.6/site-packages/gi/overrides/GLib.py", line 172, in _new_
v = creator._create(format_string, value)
File "/usr/lib64/python3.6/site-packages/gi/overrides/GLib.py", line 150, in _create
builder.add_value(self._create(dup, i))
File "/usr/lib64/python3.6/site-packages/gi/overrides/GLib.py", line 118, in _create
return self._LEAF_CONSTRUCTORS[format](value)
TypeError: Argument 0 does not allow None as a value
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

This makes it harder to recover system installations.

Version-Release number of selected component (if applicable):

anaconda from RHEL8.6+ (not tested with more ancient DVDs)

How reproducible:

Always

Steps to Reproduce:
1. Comment out "/" (e.g. "/dev/mapper/rhel-root") entry in /etc/fstab
2. Boot in Troubleshoot Mode
3. Select "1) Continue"

Actual results:

See above

Expected results:

No crash and getting prompt