Index: lib/synchronizer.js
===================================================================
--- a/lib/synchronizer.js
+++ b/lib/synchronizer.js
@@ -281,18 +281,16 @@
     for (let line of lines)
     {
       line = Filter.normalize(line);
       if (line)
         filters.push(Filter.fromText(line));
     }
 
     FilterStorage.updateSubscriptionFilters(subscription, filters);
-
-    return undefined;
   },
 
   _onDownloadError(downloadable, downloadURL, error, channelStatus,
                    responseStatus, redirectCallback)
   {
     let subscription = Subscription.fromURL(downloadable.url);
     subscription.lastDownload = Math.round(Date.now() / MILLIS_IN_SECOND);
     subscription.downloadStatus = error;