Unitofmeasure.php

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */

namespace Magento\Fedex\Model\Source;

class Unitofmeasure extends Generic
{
    /**
     * Carrier code
     *
     * @var string
     */
    protected $_code = 'unit_of_measure';
}