title: Mongoose object :javascript map function not working on adding new keys
body: <p>I am trying to add a new key on the JSON array return from the mongoose query </p>
  
  <pre><code>  find({chatBotId:req.params.chatBotId}).
    populate('userPlan').
   .exec(function(err,result){
  
     result.map(function(e){           
        e.transactionObject =null
        e.taxAmount = 100;    
        return e;    
      });
  })
  </code></pre>
  
  <p>I am adding a new key <code>taxAmount</code> but it does not appear the array, however, <code>transactionObject=null</code> works fine it's an existing key</p>