- Patch #774218 by jhedstrom: the RDFa markup for custom image field is invalid.

modules/rdf/rdf.module

@@ -548,7 +548,7 @@ function rdf_preprocess_field(&$variables) {
       // the file. We correct this by adding a resource attribute to the div if
       // this field has a URI.
       if (isset($item['uri'])) {
-        if (isset($element[$delta]['#image_style'])) {
+        if (!empty($element[$delta]['#image_style'])) {
           $variables['item_attributes_array'][$delta]['resource'] = image_style_url($element[$delta]['#image_style'], $item['uri']);
         }
         else {