Zend\Diactoros\Response\InjectContentTypeTrait::injectContentType PHP Method

    private function injectContentType($contentType, array $headers)
    {
        $hasContentType = array_reduce(array_keys($headers), function ($carry, $item) {
            return $carry ?: strtolower($item) === 'content-type';
        }, false);
        if (!$hasContentType) {
            $headers['content-type'] = [$contentType];
        }
        return $headers;
    }