[fw-mvc] Zend_Form_Element_File fatal error

Hi all

I'm using the following code:

// form

$file = new Zend_Form_Element_File('avatar');
$file->setLabel(_('Avatar'));

// controller

if ($this->getRequest()->isPost())
{           
  if ($form->avatar->receive())
  {
    var_dump($form->getValues());
    die;
  }
}

but I keep getting

Fatal error: Unsupported operand types in /home/neil/www/chitter/library/Zend/File/Transfer/Adapter/Abstract.php on line 796

The code at that point is the += in

        foreach ($files as $file) {
            if (!isset($this->_files[$file])) {
                require_once 'Zend/File/Transfer/Exception.php';
                throw new Zend_File_Transfer_Exception('Unknown file');
            }
            $filters += $this->_files[$file]['filters'];
        }

But ['filters'] isn't set in my $this->_files[$file].

Am I doing something wrong?

- Neil