diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index e2c06ec..4e30cf8 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -1157,13 +1157,13 @@ function theme($hook, $variables = array()) {
       template_preprocess($default_template_variables, $hook);
       $variables += $default_template_variables;
     }
-    if (isset($variables['attributes']) && $variables['attributes'] && !($variables['attributes'] instanceof Attribute)) {
+    if (isset($variables['attributes']) && is_array($variables['attributes']) && !($variables['attributes'] instanceof Attribute)) {
       $variables['attributes'] = new Attribute($variables['attributes']);
     }
-    if (isset($variables['title_attributes']) && $variables['title_attributes'] && !($variables['title_attributes'] instanceof Attribute)) {
+    if (isset($variables['title_attributes']) && is_array($variables['title_attributes']) && !($variables['title_attributes'] instanceof Attribute)) {
       $variables['title_attributes'] = new Attribute($variables['title_attributes']);
     }
-    if (isset($variables['content_attributes']) && $variables['content_attributes'] && !($variables['content_attributes'] instanceof Attribute)) {
+    if (isset($variables['content_attributes']) && is_array($variables['content_attributes']) && !($variables['content_attributes'] instanceof Attribute)) {
       $variables['content_attributes'] = new Attribute($variables['content_attributes']);
     }
 
diff --git a/core/modules/block/lib/Drupal/block/Tests/BlockStorageUnitTest.php b/core/modules/block/lib/Drupal/block/Tests/BlockStorageUnitTest.php
index 207f20b..f0f873f 100644
--- a/core/modules/block/lib/Drupal/block/Tests/BlockStorageUnitTest.php
+++ b/core/modules/block/lib/Drupal/block/Tests/BlockStorageUnitTest.php
@@ -159,7 +159,7 @@ protected function renderTests() {
     $expected = array();
     $expected[] = '  <div id="block-test-block"  class="block block-block-test">';
     $expected[] = '';
-    $expected[] = '    <h2 class="">Powered by Bananas</h2>';
+    $expected[] = '    <h2>Powered by Bananas</h2>';
     $expected[] = '  ';
     $expected[] = '  <div class="content">';
     $expected[] = '      </div>';