I am facing an issue, while implementing model associations. here are my models

Code:
Ext.define('EPSS.model.EventType', {    extend: 'Ext.data.Model',
    uses: [
        'EPSS.model.Event'
    ],


    idProperty: 'Id',


    fields: [
        {
            name: 'Id'
        },
        {
            name: 'Name'
        },
        {
            name: 'Color'
        },
        {
            name: 'EventId'
        }
    ]
});

Ext.define('EPSS.model.Event', {
    extend: 'Ext.data.Model',
    uses: [
        'EPSS.model.EventType'
    ],


    idProperty: 'Id',


    fields: [
        {
            name: 'Id'
        },
        {
            name: 'Name'
        },
        {
            name: 'DueDate',
            type: 'date'
        },
        {
            name: 'Status'
        },
        {
            name: 'LastModified',
            type: 'date'
        },
        {
            name: 'EventTypeId'
        }
    ],
    associations: [{
        type: 'belongsTo',
        model: 'EPSS.model.EventType',
        associatedName: 'EventType',
        instanceName: 'EventType'
    }],


    proxy: {
        type: 'rest',
        url: '/epss/api/Event',
        reader: {
            type: 'json',
            root: 'data'
        }
    }
});
Here is the json data

Code:
{
DueDate: "/Date(1338922800000+0500)/",
  EventType: {
   Color: "green",
Id: 1,
Name: "Begining of Year"
},
EventTypeId: 1,
Id: 1,
LastModified: "/Date(1275332400000+0500)/",
Name: "Event 1",
Status: "approved" 
}
when I execute following line of code...

var row = store.getAt(0);


row.getEventType(function (event) {

}, this);

following exception is thrown

Uncaught TypeError: undefined is not a function