Index: wp-content/themes/twentytwelve/js/navigation.js
===================================================================
--- wp-content/themes/twentytwelve/js/navigation.js	(revision 22323)
+++ wp-content/themes/twentytwelve/js/navigation.js	(working copy)
@@ -4,6 +4,9 @@
  * Handles toggling the navigation menu for small screens.
  */
 ( function() {
+	if ( null === document.getElementById( 'site-navigation' ) )
+		return false;
+
 	var button = document.getElementById( 'site-navigation' ).getElementsByTagName( 'h3' )[0],
 	    menu   = document.getElementById( 'site-navigation' ).getElementsByTagName( 'ul' )[0];