function toRaw()
    {
        $subfields = array();
        foreach ($this->subfields as $subfield) {
            if (!$subfield->isEmpty()) {
                $subfields[] = $subfield->toRaw();
            }
        }
        return (string)$this->ind1.$this->ind2.implode("", $subfields).File_MARC::END_OF_FIELD;
    }