Description of problem:
Start PXE installation on VM with single 20 GB disk (not empty) with this kickstart:

lang en_US.UTF-8
clearpart --all --drives=sda

Add iscsi disk (9GB), check it to be used.
In INSTALLATION DESTINATION switch from "Automatic" to "Custom", click "Done"

Version-Release number of selected component:
anaconda-32.24.2

The following was filed automatically by anaconda:
anaconda 32.24.2 exception report
Traceback (most recent call first):
  File "/usr/lib/python3.8/site-packages/dasbus/client/handler.py", line 496, in _handle_method_error
    raise exception from None
  File "/usr/lib/python3.8/site-packages/dasbus/client/handler.py", line 474, in _get_method_reply
    return self._handle_method_error(error)
  File "/usr/lib/python3.8/site-packages/dasbus/client/handler.py", line 442, in _call_method
    return self._get_method_reply(
  File "/usr/lib64/python3.8/site-packages/pyanaconda/ui/gui/spokes/storage.py", line 879, in _check_disk_selection
    self._disk_select_module.ValidateSelectedDisks(self._selected_disks)
  File "/usr/lib64/python3.8/site-packages/pyanaconda/ui/gui/spokes/storage.py", line 803, in on_back_clicked
    if not self._check_disk_selection():
dasbus.error.DBusError: 'NoneType' object has no attribute 'isleaf'

Additional info:
addons:         com_redhat_kdump
cmdline:        /usr/bin/python3  /sbin/anaconda
cmdline_file:   initrd=test/rv/scripted/development-f32/initrd.img repo=http://download.englab.brq.redhat.com/pub/fedora/development/32/Everything/x86_64/os/ ks=http://10.43.136.2/ks/rv/ks.partcrash.cfg BOOT_IMAGE=test/rv/scripted/development-f32/vmlinuz 
executable:     /sbin/anaconda
hashmarkername: anaconda
kernel:         5.6.0-0.rc3.git0.1.fc32.x86_64
product:        Fedora
release:        Fedora release 32 (Thirty Two)
release_type:   pre-release
type:           anaconda
version:        32