src/Http/Formatting/RequestHeaderParser.php
public function parseContentTypeHeader(HttpHeaders $headers): ?ContentTypeHeaderValue
    {
        if (!$headers->containsKey('Content-Type')) {
            return null;
        }

        $contentTypeHeaderParameters = $this->parseParameters($headers, 'Content-Type');
        $contentType = $contentTypeHeaderParameters->getKeys()[0];

        return new ContentTypeHeaderValue($contentType, $contentTypeHeaderParameters);
    }
public function parseContentTypeHeader(HttpHeaders $headers): ?ContentTypeHeaderValue
    {
        if (!$headers->containsKey('Content-Type')) {
            return null;
        }

        $contentTypeHeaderParameters = $this->parseParameters($headers, 'Content-Type');
        $contentType = $contentTypeHeaderParameters->getKeys()[0];

        return new ContentTypeHeaderValue($contentType, $contentTypeHeaderParameters);
    }
Parses the Content-Type header

@param HttpHeaders $headers The request headers to parse
@return ContentTypeHeaderValue|null The parsed header if one exists, otherwise null
@throws InvalidArgumentException Thrown if the headers were incorrectly formatted