Ticket #23539: 23539.2.diff

wp-includes/revision.php

@@ -523 +523 @@
                 return $value;
 
         $preview = wp_get_post_autosave( $post->ID );
+        if ( ! is_object( $preview ) )
+                return $value;
+
         return get_post_meta( $preview->ID, $meta_key, $single );
 }