Magento 1.8 – Retrieve Event Observer Data After Saving Category

I want to export data of a category when its save in magento system. So, I also create a module & create a event name which is catalog_category_save_commit_after.
My code is like below..

<config>
<global>
 ....
<events>
        <catalog_category_save_commit_after>
            <observers>
                <category_category_observer>
                    <type>singleton</type>
                    <class>Feed_Category_Model_Category_Observer</class>
                    <method>saveCategoryData</method>
                </category_category_observer>
            </observers>
        </catalog_category_save_commit_after>
    </events>
</global>

class Feed_Category_Model_Category_Observer
{
    public function saveCategoryData($observer)
    {              

        $category = $observer->getEvent()->getDataObject();
        Mage::log($category);
        // or
        Mage::log($observer->getEvent()->getCategory());    

    }
 }

Both are return blank. Have any idea??