diff -u b/core/modules/views/templates/views-view-summary-unformatted.html.twig b/core/modules/views/templates/views-view-summary-unformatted.html.twig
--- b/core/modules/views/templates/views-view-summary-unformatted.html.twig
+++ b/core/modules/views/templates/views-view-summary-unformatted.html.twig
@@ -9,7 +9,7 @@
  *   - count: The number of items this summary item represents.
  *   - separator: A separator between each row.
  *   - attributes: HTML attributes for a row.
- *   - active: A flag indicating whtether the row is active.
+ *   - active: A flag indicating whether the row is active.
  * - options: Flags indicating how each row should be displayed. This contains:
  *   - count: A flag indicating whether the row's 'count' should be displayed.
  *   - inline: A flag indicating whether the item should be wrapped in an inline
diff -u b/core/modules/views/views.theme.inc b/core/modules/views/views.theme.inc
--- b/core/modules/views/views.theme.inc
+++ b/core/modules/views/views.theme.inc
@@ -771,7 +771,7 @@
   $style = $view->style_plugin;
   $options = $style->options;
 
-  $variables['default_row_class'] = isset($options['default_row_class']) ? $options['default_row_class'] : FALSE;
+  $variables['default_row_class'] = !empty($options['default_row_class']);
   foreach ($rows as $id => $row) {
     $variables['rows'][$id] = array();
     $variables['rows'][$id]['content'] = $row;