Index: services.module
===================================================================
--- services.module	(.../orig/current/sites/all/modules/services)	(revision 3357)
+++ services.module	(.../trunk/sites/all/modules/services)	(revision 3357)
@@ -349,7 +349,7 @@
   $hash_parameters = array();
   foreach ($method['#args'] as $key => $arg) {
     if (!$arg['#optional']) {
-      if (!is_numeric($args[$key]) && empty($args[$key])) {
+      if (!isset($args[$key])) {
         return services_error(t('Missing required arguments.'));
       }
     }