add: if (fetcher._callback) fetcher._callback(responseText); 
context:   readyStateChange: function(fetcher) {    if (fetcher._request.readyState != 4) // TODO: check status code 200      return;    // We occasionally get an NS_ERROR_NOT_AVAILABLE (it doesn't have    // headers) when we try to read the response. Mask the exception    // by returning null response.     // TODO maybe masking this should be an option?    try {      G_Debug(this, "xml fetch status code: \"" +               fetcher._request.status + "\"");      if (fetcher._callback)        fetcher._callback(fetcher._request.responseText);    } catch(e) {      G_Debug(this, "Caught exception trying to read xmlhttprequest " +              "status/response.");      G_Debug(this, e);      if (fetcher._callback)        fetcher._callback(null);    }  }
meta: 9421	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/9421/9d99105501d7a39f2b6da251e05b5bc7cfab24ce/xml-fetcher.js/buggy/toolkit/components/url-classifier/content/xml-fetcher.js