Unhandled Error!

Trying to get property of non-object

Document	Product
Document type	CMS page
Line	5
Exception class	Cms_ExecutionException

Code Highlight

  <div id="content_outer" class="container_24 clearfix">
 
    <div id="side_nav" class="grid_5">
 
      <? $product_categories = $product->category_list;
        //$product_main_cat = $product->category_list[0];
        //$product_sub_cat = $product->category_list[1];
        foreach ($product_categories as $product_category) :
          if ( !( $product_category->get_parent() )) :
            $product_main_cat = $product_category;
          endif;
        endforeach;
      ?>

#	Document	Type
1	Product	CMS page