Index: wp-includes/user.php
===================================================================
--- wp-includes/user.php	(revision 17089)
+++ wp-includes/user.php	(working copy)
@@ -389,6 +389,7 @@
 				'offset' => '', 'number' => '',
 				'count_total' => true,
 				'fields' => 'all',
+				'who' => '',
 			) );
 
 			$this->prepare_query();