How to force ember data to reset all fields of a record on reload?

I am using ember with ember data and i have a scenario where I need to reload a model. On reload, when the data is fetched and some fields of that model are null, the older data still persists. For eg., if I have a Post model

App.Post = DS.Model.extend({
  name: DS.attr('string'),
  description: DS.attr('string'),
});

Now the first time the server returns the following data:

{
  "post" : {
              "id" : "1",
              "name" : "new post",
              "description": "some description"
           }
}

After reload is called, the server returns the following data:

{
  "post" : {
              "id" : "1",
              "name" : "new post",
           }
}

So after the reload, "description" field should be set to null for that record. But the old data ie., "some description" still persists in that field.

How can I force ember data to reset all fields on reload?