add: if (myFilterList) { numOfFilters = myFilterList.filterCount; } else return false;  
context: function isDuplicateFilterNameExists(){    var args = window.arguments[0];    var myFilterList = args.filterList;    var numOfFilters = myFilterList.filterCount;    var filterName= gFilterNameElement.value;    var currentFilter;    var alreadyExists = false;    for (var i = 0; i < numOfFilters; i++)    {        currentFilter = (myFilterList.getFilterAt(i)).filterName;        if (filterName == currentFilter)        {            alreadyExists = true;            break;        }    }    if (alreadyExists)        return true;    else        return false;}
meta: 8395	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/8395/2914e8ec89e97854cf0d259c68e3b40af74fd142/FilterEditor.js/clean/mailnews/base/search/resources/content/FilterEditor.js