add: if (!hosts) continue;  
context:   _updatePermissions: function ()  {    try {      var ioService = Components.classes["@mozilla.org/network/io-service;1"]                                .getService(Components.interfaces.nsIIOService);      var pbi = Components.classes["@mozilla.org/preferences-service;1"]                          .getService(Components.interfaces.nsIPrefBranch2);      var prefList = [["xpinstall.whitelist.add", nsIPermissionManager.ALLOW_ACTION],                      ["xpinstall.whitelist.add.103", nsIPermissionManager.ALLOW_ACTION],                      ["xpinstall.blacklist.add", nsIPermissionManager.DENY_ACTION]];      for (var i = 0; i < prefList.length; ++i) {        try {          // this pref is a comma-delimited list of hosts          var hosts = pbi.getCharPref(prefList[i][0]);        } catch(ex) {          continue;        }        hostList = hosts.split(",");        var capability = prefList[i][1];        for (var j = 0; j < hostList.length; ++j) {          // trim leading and trailing spaces          var host = hostList[j].replace(/^\s*/,"").replace(/\s*$/,"");          try {            var uri = ioService.newURI("http://" + host, null, null);            this._pm.add(uri, this._type, capability);          } catch(ex) { }        }        pbi.setCharPref(prefList[i][0], "");      }    } catch(ex) { }  },
meta: 10234	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/10234/21e8cd0e058309d9e97aa09ff1c64d73d75859b0/permissions.js/clean/browser/components/preferences/permissions.js