Polymorphic Association

[HassanJ]

I have been using Rabl and I thought I should give rabl-rails a try as it promises faster responses.
I am using public_activity gem which has a polymorphic belongs_to
belongs_to :trackable, :polymorphic => true

When I use child :trackable while using rabl, everything works as expected, and the key of the child object is actually the model name. But in rabl-rails the key comes as it is, i-e 'trackable' and its empty.

An example
with rable

{
    "type": "Event",
    "users": [{
        "id": 898,
    }],
    "time": "2013-09-10T15:31:12Z",
    "event": {
        "id": 27,
        "name": "Hold it",
    }
}

with rabl-rails

{
    "type": "Event",
    "users": [{
        "id": 898,
    }],
    "time": "2013-09-10T15:31:12Z",
    "trackable": null
}