add: return null; 
context:   getIntPref: function (aPrefName, aDefVal)    {      try        {          return this.mPrefService.GetIntPref(aPrefName);        }      catch(e)        {          return aDefVal != undefined ? aDefVal : null;        }    },
meta: 10234	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/10234/b6249a8f38a50426fc1b1cca10eceb5eb63cf981/nsUserSettings.js/clean/xpfe/global/resources/content/nsUserSettings.js