title: Cannot read property of undefined when passing Static property values to class definition in ExtJS
body: <p>I was was wondering whether someone could give some help with a peculiar problem that I am having in ExtJS 4. I have a defined a store that takes some of the values that I have specified in the 'read' and 'create' properties of the api object in the proxy from a class where these values are defined in the statics section of the class. However, when I run the app, I keep getting the error:</p>
  
  <p><code>**Uncaught TypeError: Cannot read property 'Url' of undefined**.</code></p>
  
  <p>Here is the store</p>
  
  <pre><code>Ext.define('MyApp.store.address.AddressStore',
         {
             extend: 'Ext.data.Store',
             model: 'MyApp.model.address.AddressModel',
             requires: ['MyApp.props.Url'],
             proxy: {
                 type: 'ajax',
                 api: {
                     create: MyApp.props.Url.Address.ADD_ADDRESS_URL, //This is defined in the static class below
                     read: MyApp.props.Url.Address.GET_ALL_ADDRESSES_URL //As is this
  
                 },
                 reader: {
                     type: 'json',
                     root: 'Addresses'
                 }
             }
         }
  
        );
  </code></pre>
  
  <p>Heres is the the class that defines the static properties MyApp.props.Url</p>
  
  <pre><code>Ext.define('MyApp.props.Url', {
      statics: {
          Address: {
             ADD_ADDRESS_URL: 'Address/AddAddress',
             GET_ALL_ADDRESSES_URL: 'Address/GetAllAddresses',
             GET_ALL_ADDRESS_TYPES_URL: 'Address/GetAllAddressTypes'
          }
  }
  </code></pre>
  
  <p>});</p>