Show members from a specific membership ID in WPMU Membership2

code.php

<?php

/**
 * Usage: [show_members id="XX"] where XX is the membership ID
 */

add_shortcode( 'show_members', 'show_members_cb' );
function show_members_cb( $atts ) {
    $atts = shortcode_atts(
        array(
            'id' => 0
        ),
        $atts
    );

    if( $atts['id'] == 0 ) {
        return 'You need to provide a membership ID';
    }

    $args = array(
        'membership_id' => $atts['id'],
        'subscription_status' => 'active'
    );
    $members = MS_Model_Member::get_members( $args );
    $html = '<table cellpadding="5" cellspacing="5">';
        $html .= '<tr>';
            $html .= '<th>User ID</th>';
            $html .= '<th>Username</th>';
            $html .= '<th>Display Name</th>';
        $html .= '</tr>';
    foreach( $members as $member ) {
        $html .= '<tr>';
            $html .= '<td>' . $member->id . '</td>';
            $html .= '<td>' . $member->username . '</td>';
            $html .= '<td>' . $member->name . '</td>';
        $html .= '</tr>';
    }
    $html .= '</table>';

    return $html;
}