Description of problem:
PXE installation with a kickstart:

PXE boot parameters to initramfs:  append initrd=initrd-x86_64.img ip=dhcp ks=ftp://172.18.2.4/ks.cfg inst.stage2=ftp://172.18.2.4/os-x86_64 slub_debug=

kickstart:

rootpw letmein
install
#url --url http://172.18.2.3/fedora

#ftp --server=192.168.10.1
#nfs --server=172.18.2.4 --dir=/var/lib/libvirt/images
lang en_US.UTF-8
#network --device eth0 --bootproto static
# --bootproto dhcp
selinux --disabled

%pre
%end

firewall --disabled
authconfig --enableshadow --enablemd5
#keyboard 'us'
timezone --utc America/Toronto
zerombr
clearpart --all --drives=vda
part /boot --fstype ext2 --size=300 --asprimary
part / --fstype ext2 --grow --size=1024 --asprimary
bootloader --location=mbr --driveorder=vda --timeout=5

%packages --nobase --excludedocs
@Standard
kernel
grub2
-sendmail
net-tools
chrony
%end

%post --log=/root/dump.log
echo "Disabling services: mcelog, smartd, firewalld, atd, crond"
chkconfig mcelog off
chkconfig smartd off
chkconfig firewalld off
chkconfig atd off
chkconfig crond off
chkconfig chronyd on

echo "1 letmein" >> /etc/chrony.keys
%end

Set the keyboard to US manually, then tried to select installation source, Anaconda crashed.

Version-Release number of selected component:
anaconda-20.8-1

The following was filed automatically by anaconda:
anaconda 20.8-1 exception report
Traceback (most recent call first):
  File "/usr/lib64/python2.7/site-packages/pyanaconda/ui/gui/spokes/source.py", line 651, in refresh
    if proto.startswith("http:"):
  File "/usr/lib64/python2.7/site-packages/pyanaconda/ui/gui/hubs/__init__.py", line 108, in _runSpoke
    action.refresh()
  File "/usr/lib64/python2.7/site-packages/pyanaconda/ui/gui/hubs/__init__.py", line 413, in _on_spoke_clicked
    self._runSpoke(spoke)
AttributeError: 'NoneType' object has no attribute 'startswith'

Additional info:
cmdline:        /usr/bin/python  /sbin/anaconda
cmdline_file:   initrd=initrd-x86_64.img ip=dhcp ks=ftp://172.18.2.4/ks.cfg inst.stage2=ftp://172.18.2.4/os-x86_64 slub_debug=- BOOT_IMAGE=vmlinuz-x86_64 
executable:     /sbin/anaconda
hashmarkername: anaconda
kernel:         3.11.0-0.rc6.git4.1.fc20.x86_64
product:        Fedora
release:        Cannot get release name.
type:           anaconda
version:        20-Alpha-TC1