Merge pull request #61 from jonathanong/onerror-condition

onerror: check existence of error

lib/context.js

@@ -644,6 +644,11 @@ module.exports = {
    */
 
   onerror: function(err){
+    // don't do anything if there is no error.
+    // this allows you to pass `this.onerror`
+    // to node-style callbacks.
+    if (!err) return;
+
     // nothing we can do here other
     // than delegate to the app-level
     // handler and log.