another attempt at fixing preset argument

config.lua

@@ -1,4 +1,5 @@
-local preset = rawget(_G, 'preset') or 'ars'
+local preset = rawget(_G, 'preset')
+preset = preset ~= nil and preset ~= '' and preset or 'ars'
 
 local common_cfg = {
     -- read-only modes:

main.lua

@@ -1,4 +1,4 @@
-preset = arg -- must be done before requiring strict!
+preset = arg or "" -- must be done before requiring strict!
 local globalize = require("strict")
 
 -- configuration.