Core_Upload::__construct

public function __construct($file_key = null)
{
    if (null===$file_key)
    {
        $file = $_FILES;
        $file = current($file);
    }
    else
    {
        $file = $_FILES[$file_key];
    }

    if (!$file)
    {
        throw new Exception('Upload userfile not set.', UPLOAD::ERR_NO_FILE);
    }

    $this->file = $file;
}