"Cannot access empty property"

Az alábbi hibaüzenettel fogad egyik honlapom:

Fatal error: Cannot access empty property in /home2/hirugyno/public_html/szucsag/sites/all/modules/views/modules/node.views.inc on line 670

Ez mit jelenthet?
Az említett sorok ezek: **
* Template helper for theme_views_view_row_node
*/
function template_preprocess_views_view_row_node(&$vars) {
$options = $vars['options'];

// Make sure the variables are defined.
$vars['node'] = '';
$vars['comments'] = '';

(670. sor) $nid = $vars['row']->{$vars['field_alias']};
if (!is_numeric($nid)) {
return;
}

$node = node_load($nid);

if (empty($node)) {
return;
}