Ember RESTAdapter - hasMany relationship in model - how to send empty array with POST?

Ember noob here -

I have two models with a hasMany relationship like below -

var Season = DS.Model.extend({
    name: DS.attr('string'),
    periods: DS.hasMany('period', {
        async: false
    })
});

var Period = DS.Model.extend({
    from: DS.attr('date'),
    to: DS.attr('date'),
    season: DS.belongsTo('season')
});

A Season can exist without any Periods - This is how I create a Season record and save --

        var season = this.store.createRecord('season', {
            name: name
        });

        season.save().then(function(season){
                   /* season saved */
        });

The POST request payload looks like this --

   {
    "season" : {
         "name" : "test"
     }
   }

But the backend API expects the payload to be like this -- with an empty periods array

    {
    "season" : {
         "name" : "test"
         "periods" : []
     }
   }

How do I achieve this?