# Returns argument `arg_name` in the request as a String
	# or null if it was not found.
	# Also cleans the String by trimming it.
	# If the Strings happens to be empty after trimming,
	# the method will return `null`
	#
	# NOTE: Prioritizes POST before GET
	fun string_arg(arg_name: String): nullable String do
		if not all_args.has_key(arg_name) then return null
		var s = all_args[arg_name].trim
		if s.is_empty then return null
		return s
	end