fixed calling registered objects' methods with an empty argument list.

thanks marcello

NEWS

@@ -1,3 +1,5 @@
+- fix calling registered objects' methods with an empty argument list
+  (marcello, messju)
 - fix html_select_date separator when parts are missing (hayk,
   monte)
 - fix broken detection of non-cached blocks introduced in 2.6.17

libs/Smarty_Compiler.class.php

@@ -869,7 +869,7 @@ class Smarty_Compiler extends Smarty {
             // traditional argument format
             $args = implode(',', array_values($attrs));
             if (empty($args)) {
-                $args = 'null';
+                $args = '';
             }
         }