add: return null; 
context: function get_sidebar_datasource_uri() {  try {    var sidebar_file = sidebar_get_panels_file();    var file_url = Components.classes["component://netscape/network/standard-url"].createInstance(Components.interfaces.nsIFileURL);    file_url.file = sidebar_file;    return file_url.spec;  } catch (ex) {    // This should not happen    debug("Error: Unable to load panels file.\n");    return null;  }}
meta: 9421	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/9421/a3fd1360f8a3ed6857cc435f9c9b5e8b3cdd9ef2/sidebarOverlay.js/clean/xpfe/components/sidebar/resources/sidebarOverlay.js