some args are optional, do not return errors

actions/dynamicDNS

@@ -75,10 +75,6 @@ doGetOpt()
                 echo "Invalid option: -$OPTARG" >&2
                 exit 1
             ;;
-            :)
-                echo "Option -$OPTARG requires an argument." >&2
-                exit 1
-            ;;
         esac
     done
 }
@@ -256,6 +252,7 @@ case $cmd in
         echo "clean                   delete configuration"
         echo "success                 store update success"
         echo "failed                  store update failure"
+        echo "get-nat                 return the detected nat type"
     ;;
 esac
 exit 0