Index: src/wp-admin/includes/user.php
===================================================================
--- src/wp-admin/includes/user.php	(revision 25200)
+++ src/wp-admin/includes/user.php	(working copy)
@@ -195,12 +195,13 @@
  * @since 2.0.5
  *
  * @param int $user_id User ID.
- * @return object WP_User object with user data.
+ * @return bool|WP_User False on failure, WP_User object on success.
  */
 function get_user_to_edit( $user_id ) {
 	$user = get_userdata( $user_id );
 
-	$user->filter = 'edit';
+	if ( $user )
+		$user->filter = 'edit';
 
 	return $user;
 }