title: MAGENTO: Getting fatal error after overriding a module using my custom module
body: <p>I am newbie in Magento, so I need your help in finding a solution.</p>
  
  <p>I am overriding one module file: app\code\core\Mage\Sales\Model\Quote\item.php</p>
  
  <p>config.xml sample code:</p>
  
  <pre><code>&lt;global&gt;
      &lt;models&gt;
          &lt;sales&gt;
              &lt;rewrite&gt;
                  &lt;quote_item&gt;Module_Name_Model_Sales_Quote_Item&lt;/quote_item&gt;
              &lt;/rewrite&gt;
        &lt;/sales&gt;
     &lt;/models&gt;
  &lt;/global&gt;
  </code></pre>
  
  <hr>
  
  <p>My item.php file contain only the class name which extend the class that i need to override:</p>
  
  <pre><code>class Module_Name_Model_Sales_Model_Quote_Item extends Mage_Sales_Model_Quote_Item 
  {
  
  }
  </code></pre>
  
  <hr>
  
  <p>Even i have not yet override any method in item.php am getting the following error when i open my website in a browser.</p>
  
  <pre><code>Fatal error: Call to a member function getCollection() on a non-object in C:\Sites\porcani\branches\development\app\code\core\Mage\Sales\Model\Quote.php on line 706
  </code></pre>
  
  <p>Anyone have an idea why this is happening and how to solve it? Thanks in Advance.</p>