Index: wp-includes/plugin.php
===================================================================
--- wp-includes/plugin.php	(revision 12261)
+++ wp-includes/plugin.php	(working copy)
@@ -318,7 +318,7 @@
 	}
 
 	$args = array();
-	if ( is_array($arg) && 1 == count($arg) && is_object($arg[0]) ) // array(&$this)
+	if ( is_array($arg) && 1 == count($arg) && isset($arg[0]) && is_object($arg[0]) ) // array(&$this)
 		$args[] =& $arg[0];
 	else
 		$args[] = $arg;