final public function serializeXml(array $fields)
    {
        $className = $this->stripNamespaceFromClassName($this);
        $output = '<'.$className.'>';
        foreach ($fields as $key => $value) {
            if (empty($value)) {
                continue;
            }
            // Unnecessary fields
            $key = str_replace(' ', '_', ucwords(str_replace(['_', '$', '%5F', '?'], [' ', 'N36', 'E5F', '98T'], $key)));
            $output .= '<'.$key.'>'.htmlspecialchars($value).'</'.$key.'>';
        }
        $output .= '</'.$className.'>';

        return $output;
    }