调用查询时返回的Salesforce不是预期对象

我正在使用force-php工具包从salesforce获取一些对象。我有以下代码:

$mySforceConnection = new SforcePartnerClient();
$mySoapClient = $mySforceConnection->createConnection(SOAP_CLIENT_BASEDIR.'/partner.wsdl.xml');
$mylogin = $mySforceConnection->login(USERNAME, PASSWORD.SECURITY_TOKEN);
$query = "SELECT FirstName from Contact";
$response = $mySforceConnection->query($query);
$queryResult = new QueryResult($response);
foreach ($queryResult->records as $record) {
    print_r($record);
    echo "<br/>";
}

和我期望以这种形式返回的对象:

stdClass Object
(
[type] = Contact
[Id] = Array
    (
        [0] => 003i0000009GZVzAAO
        [1] => 003i0000009GZVzAAO
    )
[FirstName] = "Some String" 
[any] = <sf:firstname>Some String</sf:firstname>
)

所以我可以得到对象的FirstName记录-> FirstName

但是我得到的是:

stdClass Object
(
[type] = Contact
[Id] = Array
    (
        [0] => 003i0000009GZVzAAO
        [1] => 003i0000009GZVzAAO
    )
[any] = <sf:firstname>Some String</sf:firstname>
)

所以我不能得到FirstName。我可以访问的唯一属性是'any'。我怎样才能得到一个预期的对象?我应该关注哪里?