title: Mongoose : error returned is empty object
body: <p>what am I doing wrong?
  Try to save a new Entry via findOneAndUpdate.</p>
  
  <pre><code>Offer.findOneAndUpdate(conditions,payload,{upsert:true,new: true},function(err, offer) {
      if(err){
              response.status(500).send({"message": "This is an error! Can not save _offer", "error":err, "payload":payload});
      }else{
              response.status(200).send(offer);
      }
  });
  </code></pre>
  
  <p>but I got permanently Error 500 with error = {}</p>
  
  <blockquote>
    <p>{"message":"This is an error! Can not save
    _offer","error":{},"payload":{"foo":"bar"}}</p>
  </blockquote>
  
  <p>What can I do?</p>