Magento 2 Plugin Error – Missing Argument 2

Based on certain aspects of an order I want to replace the email template being used. I'd preferably like to use a plugin to do this as I feel this is the proper Magento 2 way.

Unfortunately most of the methods i'd like to intercept are protected. Thanks Magento. Anyway, the soonest place I can find to do this is in Magento\Sales\Model\Order\Email\SenderBuilder and using a plugin before the send() method.

I'm getting the error :

Missing argument 2 for 
 Namespace\Moduename\Model\Plugin\ReplaceNewOrderEmailPlugin::beforeSend(), 
called in /var/www/public/vendor/magento/framework/Interception/Interceptor.php on line 123 
and defined in /var/www/public/vendor/namespace/modulename/Model/Plugin/ReplaceNewOrderEmailPlugin.php on line 9

Here is my code :

di.xml

<type name="Magento\Sales\Model\Order\Email\SenderBuilder">
        <plugin name="Company_Namespace::ReplaceNewOrderEmail"
                type="Company\Namespace\Model\Plugin\ReplaceNewOrderEmailPlugin"
                sortOrder="10"
                disabled="false"/>
    </type>

Plugin file

use Magento\Sales\Model\Order\Email\SenderBuilder;

class ReplaceNewOrderEmailPlugin
{

    public function beforeSend($subject, $result)
    {
        die('plugin working');
        return $result;
    }
}

and for good measure, here is the function i'm trying to plugin to

public/vendor/magento/module-sales/Model/Order/Email/SenderBuilder.php

public function send()
    {
        $this->configureEmailTemplate();

        $this->transportBuilder->addTo(
            $this->identityContainer->getCustomerEmail(),
            $this->identityContainer->getCustomerName()
        );

        $copyTo = $this->identityContainer->getEmailCopyTo();

        if (!empty($copyTo) && $this->identityContainer->getCopyMethod() == 'bcc') {
            foreach ($copyTo as $email) {
                $this->transportBuilder->addBcc($email);
            }
        }

        $transport = $this->transportBuilder->getTransport();
        $transport->sendMessage();
    }

Does anyone have any ideas why i'm getting this ?