Fix a failing bats test

Author: scottchiefbaker

diff-so-fancy

@@ -526,6 +526,7 @@ sub should_print_unicode {
 
 	# Otherwise, assume we're piping to less(1)
 	my ($less_env_var, $less_charset) = get_less_charset();
+	$less_charset //= "";
 	if ($less_charset =~ /utf-?8/i) {
 		return 1;
 	}