Ticket #20776: 20776.diff

wp-includes/plugin.php

@@ -399 +399 @@
 
         do {
                 foreach ( (array) current($wp_filter[$tag]) as $the_ )
-                        if ( !is_null($the_['function']) )
+                        if ( is_callable($the_['function']) )
                                 call_user_func_array($the_['function'], array_slice($args, 0, (int) $the_['accepted_args']));
 
         } while ( next($wp_filter[$tag]) !== false );