Using core_webservice_get_site_info with SOAP

Hi,

I am trying to write a small script using SOAP to get the contents of core_webservice_get_site_info call. The code I wrote is:

<?php
    // Declares
    $token = "638bfd64ea2a087de2cb514dab1efbcc";
    $serverUrl = "http://<my_moodle_url>/webservice/soap/server.php?wsdl=1&wstoken=" . $token;

    $functionname = 'core_webservice_get_site_info';

    echo "<pre>\n";

    // Soap client object
    $client = new SoapClient($serverUrl);

    // Execution and output
    try {
    $resp = $client->__soapCall($functionname);
    } catch (Exception $e) {
        print_r($e);
    }
    if (isset($resp)) {
        print_r($resp);
    }
    
    echo "</pre>\n";
?>

This code returns an empty output ("<pre></pre>"). Anyone knows why is this happening? I'm only curious about this call, that's not blocker for me, I just wanted to test the output.

Thank's in advance.

Pedro L.