code: protected function findRecord($data)
      {
          if (empty($data["ID"])) {
              throw new HTTPResponse_Exception("No record ID", 404);
          }
          $page = null;
          $id = $data["ID"];
          if (is_numeric($id)) {
              $page = SiteTree::get()->byID($id);
          }
          if (!$page || !$page->ID) {
              throw new HTTPResponse_Exception("Bad record ID #{$id}", 404);
          }
          return $page;
      }
docs: Find the page this form is updating
  
  @param array $data Form data
  @return SiteTree Record
  @throws HTTPResponse_Exception