Comment # 4 on bug 903747 from Josef Reidinger

Lukas - I think I discover when nil appear.
see in log

2014-11-03 16:10:00 <3> 164.99.26.27(4027) [Interpreter] modules/Kernel.rb:726
File not found /etc/modules-load.d/MODULES_LOADED_ON_BOOT.conf
2014-11-03 16:10:00 <3> 164.99.26.27(4027) [Interpreter] modules/Kernel.rb:726
Read validate failed
2014-11-03 16:10:00 <3> 164.99.26.27(4027) [Interpreter] modules/Kernel.rb:726
SCR::Read() failed

this mean that
https://github.com/yast/yast-yast2/blob/master/library/system/src/modules/Kernel.rb#L726
is set to nil, which cause failure.

So I think for fix you just need to add check if file exists xor add condition
if SCR.Read failed to assign empty array instead of nil.