In a site I'm building I want different banner images for each section of the site, and so want a page to default it's parents banner if one is not set. I have set up the following code, but I don't see anything on the page

the code is based on this archived post

In Page.php

class Page extends SiteTree {
	
	static $has_one = array(
	'BannerImage' => 'Image'
   );
.....



class Page_Controller extends ContentController {
	
	.....	
	
	
function getBannerImage() {       
             
      if(empty($BannerImage->ID)){         
         $BannerImage = $this->getParentBannerImage($this);              
      	}       
      return $BannerImage; 
   } 
    
   
   private function getParentBannerImage($CurrentPage){       
      $Parent = $CurrentPage->Parent;       
       
      if(is_object($Parent)){ 
                   
         if(!empty($BannerImage->ID)){ 
            return $BannerImage; 
            // We found the current header! Let's return it! 
         } else { 
            return $this->getParentBannerImage($Parent); 
            // We didn't find a header,so we have to call ourselves again 
         } 
          
      } else { 
         return false; 
      } 
   }
	
....

In Page.ss i'll just do something like this:

<div id="banner" style="background:url(<% control getBannerImage %>$URL<% end_control %>)"></div> 

So, it's probably something completely obvious...just not to me at the mo!