public function addMimeType($mimetype)
    {
        $mimetypes = $this->getMimeType(true);

        if (is_string($mimetype)) {
            $mimetype = explode(',', $mimetype);
        } elseif (!is_array($mimetype)) {

            throw new Zend_Validate_Exception("Invalid options to validator provided");
        }

        if (isset($mimetype['magicfile'])) {
            unset($mimetype['magicfile']);
        }

        foreach ($mimetype as $content) {
            if (empty($content) || !is_string($content)) {
                continue;
            }
            $mimetypes[] = trim($content);
        }
        $mimetypes = array_unique($mimetypes);

        // Sanity check to ensure no empty values
        foreach ($mimetypes as $key => $mt) {
            if (empty($mt)) {
                unset($mimetypes[$key]);
            }
        }

        $this->_mimetype = implode(',', $mimetypes);

        return $this;
    }