diff --git a/group/externallib.php b/group/externallib.php
index d7a5a07..b530283 100644
--- a/group/externallib.php
+++ b/group/externallib.php
@@ -1310,7 +1310,7 @@ class core_group_external extends external_api {
         return new external_function_parameters(
             array(
                 'cmid' => new external_value(PARAM_INT, 'course module id'),
-                'userid' => new external_value(PARAM_INT, 'id of user, empty for current user', VALUE_OPTIONAL, 0)
+                'userid' => new external_value(PARAM_INT, 'id of user, empty for current user', VALUE_DEFAULT, 0)
             )
         );
     }
diff --git a/notes/externallib.php b/notes/externallib.php
index 944b2fb..b697bf4 100644
--- a/notes/externallib.php
+++ b/notes/externallib.php
@@ -466,7 +466,7 @@ class core_notes_external extends external_api {
         return new external_function_parameters(
             array(
                 'courseid' => new external_value(PARAM_INT, 'course id, 0 for SITE'),
-                'userid'   => new external_value(PARAM_INT, 'user id', VALUE_OPTIONAL),
+                'userid'   => new external_value(PARAM_INT, 'user id', VALUE_DEFAULT, 0),
             )
         );
     }
diff --git a/webservice/lib.php b/webservice/lib.php
index 879c716..f7e6a28 100644
--- a/webservice/lib.php
+++ b/webservice/lib.php
@@ -1293,6 +1293,7 @@ class '.$classname.' {
         $params      = array();
         $params_desc = array();
         foreach ($function->parameters_desc->keys as $name=>$keydesc) {
+            $functiondescription =  "$function->classname::$function->methodname $name";
             $param = '$'.$name;
             $paramanddefault = $param;
             //need to generate the default if there is any
@@ -1315,7 +1316,7 @@ class '.$classname.' {
                 } else if ($keydesc->required == VALUE_OPTIONAL) {
                     // It does not make sense to declare a parameter VALUE_OPTIONAL.
                     // VALUE_OPTIONAL is used only for array/object key.
-                    throw new moodle_exception('erroroptionalparamarray', 'webservice', '', $name);
+                    throw new moodle_exception('erroroptionalparamarray', 'webservice', '', $functiondescription);
                 }
             } else { //for the moment we do not support default for other structure types
                  if ($keydesc->required == VALUE_DEFAULT) {