Using overridden class under module for the web service

[Pulman]

Hi,

I'm new Prestashop, I have tried to create a new web service resource and created a new custom module to register the resource, here is the source code:
modules/due/due.php

class Due extends Module
{
    public function __construct()
    {
        // Module information
    }

    public function install()
    {
        return parent::install() && $this->registerHook('addWebserviceResources');
    }

    public function hookAddWebserviceResources($params) {
        return [
            'members' => ['description' => 'The e-shop\'s members', 'class' => 'Member']
        ];
    }

    public function uninstall()
    {
        return parent::uninstall();
    }
}

Now, I create the MemberCore class under modules/due/override/classes/Member.php

class MemberCore extends ObjectModel
{
    /** @var int Member ID */
    public $id;

    /** @var string Lastname */
    public $lastname;

    /** @var string Firstname */
    public $firstname;

    /** @var bool True if carrier has been deleted (staying in database as deleted) */
    public $deleted = 0;

    /** @var string Object creation date */
    public $date_add;

    /** @var string Object last modification date */
    public $date_upd;

    protected $webserviceParameters = [];

    /**
     * @see ObjectModel::$definition
     */
    public static $definition = [
        'table' => 'member',
        'primary' => 'id_member',
        'fields' => [
            'firstname' => ['type' => self::TYPE_STRING],
            'lastname' => ['type' => self::TYPE_STRING],
            'date_add' => ['type' => self::TYPE_DATE],
            'date_upd' => ['type' => self::TYPE_DATE]
        ],
    ];

    /**
     * MemberCore constructor.
     *
     * @param int|null $id
     */
    public function __construct($id = null)
    {
        // It sets default value for member group even when member does not exist
        parent::__construct($id);
    }
}

Then I install the module, but seems the system cannot load the MemberCore class.
However, If I place the MemberCore class under override/classes/Member.php, it works.

Can anyone help to point me what is wrong here.

Thank you!