Return ``None`` when missing data in ``lshw`` or ``dmidecode`` output
Return ``None`` when missing data in ``lshw`` or ``dmidecode`` output

Some VMs like KVM are missing items like "Base Board Information".

Since the missing items are then not added to the JSON output, the resulting
doc may not be compatible with what Device Hub expects.  Still need to check
this.

eReuse/device-inventory,eReuse/workbench,eReuse/workbench,eReuse/device-inventory