title: Empty ExtJS model instance with 'hasOne' association
body: <p>I have two ExtJS models linked by 'hasOne' association like so:</p>
  
  <pre><code>Ext.define('MyProj.model.Car', {
      extend: 'Ext.data.Model',
  
      requires: [
          'MyProj.model.CarPassport'
      ],
  
      fields: [
          { name: 'id', type: 'int' },
          { name: 'model', type: 'string' },
          { name: 'passportId', type: 'int' }
      ],
  
      associations: [
          { type: 'hasOne', model: 'CarPassport', primaryKey: 'id', foreignKey: 'passportId', getterName: 'getCarPassport', setterName: 'setCarPassport' }
      ]
  });
  
  Ext.define('MyProj.model.CarPassport', {
      extend: 'Ext.data.Model',
  
      fields: [
          { name: 'id', type: 'int' },
          { name: 'color', type: 'string' }
      ],
  });
  </code></pre>
  
  <p>Assotiation multiplicity is 1 to 1 - car cannot exist without car passport.
  When i'm trying to create empty Car instance, ExtJS doesn't add linked entity to primary entity:</p>
  
  <pre><code>var car = Ext.ModelManager.getModel('MyProj.model.Car').create();
  car.getCarPassport(); // This string produce error - getCarPassport is undefined
  </code></pre>
  
  <p>So, is it possible to create Car model instance with linked CarPassport model instance, and if true, how?
  Thanks...</p>