protected function getSimpleHeaders()
    {
        $out = [];
        foreach ($this->headers as $key => $values) {
            $header = $this->headerNames[strtolower($key)];
            if (count($values) === 1) {
                $values = $values[0];
            }
            $out[$header] = $values;
        }

        return $out;
    }