add: filter = null; 
context: function currentFilter(){    if (gFilterTree.currentIndex == -1)        return null;        var filter;    try {        filter = gFilterTree.builderView.getResourceAtIndex(gFilterTree.currentIndex);        filter = filter.GetDelegate("filter", Components.interfaces.nsIMsgFilter);    } catch (ex) {    }    return filter;}
meta: 10234	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/10234/35dcce26ded7fabe3204f81d9766214596b03898/FilterListDialog.js/buggy/mailnews/base/search/resources/content/FilterListDialog.js