backout filter of Nil UUID as the boot loader code already filters out Nil UUIDs (see src/sys/boot/i386/libi386/smbios.c:smbios_setuuid for details)

etc/rc.d/hostid

@@ -59,11 +59,7 @@ hostid_hardware()
 	uuid=`kenv smbios.system.uuid 2>/dev/null`
 	x="[0-9a-f]"
 	y=$x$x$x$x
-	z="0000"
 	case "${uuid}" in
-	$z$z-$z-$z-$z-$z$z$z)
-		# Filter the special "Nil" UUID
-		;;
 	$y$y-$y-$y-$y-$y$y$y)
 		echo "${uuid}"
 		;;