Steps to reproduce:

1. Create trigger action over API
2. Update action over API with only this parameters:

{
    "actionid": action_id,
    "operations": [
        {
            "operationtype": 0,
            "opmessage_usr": "7"
        },
    ],
}

       3. Go to web interface, Settings - Actions - Triggers

Result:

At the end of page:

• Undefined index: mediatypeid [actionconf.php:850 → CView->render() → include() → getActionOperationDescriptions() in include/actions.inc.php:401]
• Undefined index: mediatypeid [actionconf.php:850 → CView->render() → include() → getActionOperationDescriptions() in include/actions.inc.php:568]