protected function addBaseFieldset()
    {
        if (null === $this->baseFieldset) {
            return;
        }
        
        $fs = $this->baseFieldset;
        if (!is_array($fs)) {
            $fs = array(
                'type' => $fs,
            );
        }
        if (!isset($fs['options']['use_as_base_fieldset'])) {
            $fs['options']['use_as_base_fieldset'] = true;
        }
        $this->add($fs);
    }