Fixed parse errors if $firewall_rules or $firewall_custom variable is empty.

firewall/manifests/init.pp

@@ -19,6 +19,13 @@
 #
 class firewall {
 
+    if ! $firewall_custom {
+        $firewall_custom = []
+    }
+    if ! $firewall_rules {
+        $firewall_rules = []
+    }
+
     case $operatingsystem {
 	centos,fedora: {
 	    include firewall::iptables