commit 57783386c6de0eba0b9dacfb8cec903136f35d5c
Author: Joel Pittet <joel@pittet.ca>
Date:   Fri Mar 29 11:47:36 2013 -0700

    added attribute starter array

diff --git a/core/modules/block/block.module b/core/modules/block/block.module
index 95b243f..874d0de 100644
--- a/core/modules/block/block.module
+++ b/core/modules/block/block.module
@@ -554,7 +554,7 @@ function template_preprocess_block(&$variables) {
   // Create the $content variable that templates expect.
   $variables['content'] = $variables['elements']['#children'];
 
-  $variables['attributes'] = new Attribute;
+  $variables['attributes'] = new Attribute(array());
   $variables['attributes']['class'] = array();
   $variables['attributes']['class'][] = drupal_html_class('block-' . $variables['block']->module);