Warning: array_merge(): Argument #2 is not an array in

   $private_forms = array();
    if(isset($users_model->config['privforms'])){
        if (is_array($users_model->config['privforms'])){
            foreach($users_model->config['privforms'] as $form_id){
                $private_forms = array_merge($private_forms, cmsForm::getFieldsHtml($form_id, array(), true));
            }
        }
    }