htmlspecialchars（）期望参数1为字符串，COdeIgniter中的对象给定错误

When assigning a type casted array to codeigniter's session, I get this error:

A PHP Error was encountered 
Severity: Warning

Message: htmlspecialchars() expects parameter 1 to be string, object given

Filename: libraries/Profiler.php

Line Number: 514

Code in question:

$guest = array('email' => 'empty', 'username' => 'Guest');
$this->session->set_userdata(array('current_user' => (object)$guest));

The CodeIgniter profiler breaks as soon as you store any non-array non-strings in its session:

foreach ($this->CI->session->all_userdata() as $key => $val)
{
    if (is_array($val))
    {
        $val = print_r($val, TRUE);
    }

    $output .= "<...>".htmlspecialchars($val)."<...>
";
}

(from CI_Profiler::_compile_session_data())

This looks like a pretty stupid thing since print_r() works fine with objects - so is_array($val) || is_object($val) would be more appropriate.