OSXBMC http error

ASP Error: Undefined procedure isset At line 1, line => if (isset("Action")

if (isset("Action")) {
        if (Action == "UnqueMusicplaylist") {
            var ItemCount;
            var z;
            ItemCount = xbmcCommand("catalog","items");
            for (z = 0;  z < ItemCount;  z = z + 1) {
                // dirty workaround, cause unque, + z won't work
                xbmcCommand("navigate", Action);
                xbmcCommand("catalog","unque");
            }
            Action = "musicplaylist";          
        }
        xbmcCommand("navigate", Action);
    }
    
    if (isset("command")) {
        // execute a few commands before listing the contents
        if (command == "select") {
            xbmcCommand("catalog", "select," + item);
        } else if (command == "unque") {
            xbmcCommand("catalog", "unque," + item);
        }
    }

    var navigatorstate;
    var BannerClass;
    var InfoClass;
    var BackgroundClass;
    var ItemFileClass;
    navigato