diff -u b/core/modules/rdf/rdf.module b/core/modules/rdf/rdf.module
--- b/core/modules/rdf/rdf.module
+++ b/core/modules/rdf/rdf.module
@@ -567,6 +567,7 @@
  */
 function template_preprocess_rdf_metadata(&$variables) {
   foreach ($variables['metadata'] as $key => $attributes) {
+    // In some cases $attributes is unset, so we set it to an empty array.
     if (!isset($attributes)) {
       $attributes = array();
     }
diff -u b/core/modules/rdf/templates/rdf-metadata.html.twig b/core/modules/rdf/templates/rdf-metadata.html.twig
--- b/core/modules/rdf/templates/rdf-metadata.html.twig
+++ b/core/modules/rdf/templates/rdf-metadata.html.twig
@@ -15,9 +15,3 @@
 {% for attributes in metadata %}
-  {%
-    set classes = [
-      'rdf-meta',
-      'hidden',
-    ]
-  %}
-  <span{{ attributes.addClass(classes) }}></span>
+  <span{{ attributes.addClass('rdf-meta', 'hidden') }}></span>
 {% endfor %}