Loading Cache when Offline in Android Webview

I have an application which loads urls from a website. Now I want that the application to use the cache when offline. But I just get the failure page which says that im not connected to the website. At first I set the Cachemode to Load_Normal but this doesn't help. Next I tried a realy "silly" approach using the ConnectivityManager:

cm = (ConnectivityManager) this.getSystemService(Activity.CONNECTIVITY_SERVICE);
if(cm.getActiveNetworkInfo().isConnected()){
  mfnWebView.getSettings().setCacheMode(WebSettings.LOAD_DEFAULT);
  mfnWebView.loadUrl(url);
}
else{
  mfnWebView.getSettings().setCacheMode(WebSettings.LOAD_CACHE_ELSE_NETWORK);
  mfnWebView.loadUrl(url);
}

but this just leads to crashing the application.

Is there a simple way to load the cache when offline and existing and just if not existing showing the failure message.