Comment # 1 on bug 1078716 from Ancor Gonzalez Sosa

The problem is that GuidedSetup.initial was unable to create a valid proposal
(likely because /dev/vda is too small for Kubic requirements). But instead of
reporting an "storage proposal not possible" error, it crashed when trying to
assign the non-existing proposal here

https://github.com/yast/yast-storage-ng/blob/master/src/lib/y2storage/clients/partitions_proposal.rb#L163