Michael Brown
a180c7526c
[settings] Allow "set" command to take an empty value
Allow "set <variable>" to be used to set the variable to an empty
value, if permitted by the setting type. Note that some settings
backends do not differentiate between an empty value and a
non-existent value, so this may or may not be equivalent to "clear
<variable>".
Signed-off-by: Michael Brown <mcb30@ipxe.org>