ISTWCMS-4943: Update theme function to fix tests.

uw_fdsu_theme_resp.theme

@@ -400,7 +400,7 @@ function uw_fdsu_theme_resp_preprocess_block(&$variables) {
     // If node is not object by this point, probably on
     // a revision page where node is an integer, so load
     // the node.
-    if (!is_object($node)) {
+    if ($node && !is_object($node)) {
       $node = Node::load($node);
     }