Index: wp-admin/includes/dashboard.php
===================================================================
--- wp-admin/includes/dashboard.php	(revision 18138)
+++ wp-admin/includes/dashboard.php	(working copy)
@@ -1198,6 +1198,9 @@
  * @since 3.2
  */
 function wp_check_browser_version() {
+	if ( ! isset( $_SERVER['HTTP_USER_AGENT'] ) )
+		return;
+
 	$key = md5( $_SERVER['HTTP_USER_AGENT'] );
 
 	if ( false === ($response = get_site_transient('browser_' . $key) ) ) {