Fix crash when bios/raid attributes are empty in proposal

This works well when the optional attributes are non-existing, but not
when they are existing but empty.
Streamlined interface for Proposals
Merge pull request #632 from rajinir/pull-req-release-pebbles-master-7dfee8232844fe2e9e01628bf48f9a364a95919f

Streamline Interface for Proposals [1/1]
Merge pull request #618 from vuntz/crash-no-raid-bios

Fix crash when bios/raid options are empty in proposal