private function applyEtagHeader(array $options, $argName = 'etag')
    {
        if (isset($options[$argName])) {
            if (!isset($options['restOptions'])) {
                $options['restOptions'] = [];
            }

            if (!isset($options['restOptions']['headers'])) {
                $options['restOptions']['headers'] = [];
            }

            $options['restOptions']['headers']['If-Match'] = $options[$argName];
        }

        return $options;
    }