src/Http/Headers/RestrictiveHeadersChecker.php
public function checkHeaders(HeaderParametersInterface $parameters)
    {
        // Note: for these checks the order is specified by spec. See details inside.

        $this->checkAcceptHeader($parameters);

        // clients must send content type only if the request has body so there is no point in checking
        // `Content-Type` header if the original request is bodiless.
        if ($parameters->getContentTypeHeader() !== null) {
            $this->checkContentTypeHeader($parameters);
        }
    }
public function checkHeaders(HeaderParametersInterface $parameters)
    {
        // Note: for these checks the order is specified by spec. See details inside.

        $this->checkAcceptHeader($parameters);

        // clients must send content type only if the request has body so there is no point in checking
        // `Content-Type` header if the original request is bodiless.
        if ($parameters->getContentTypeHeader() !== null) {
            $this->checkContentTypeHeader($parameters);
        }
    }
@param HeaderParametersInterface $parameters

@return void