public function vacuum($data) {
		if(is_null($data)) {
			return NULL;
		} elseif(is_array($data)) {
			$ret = array();
			foreach($data as $k => $v) {
				$nv = $this->vacuum($v);
				if(isset($nv)) {
					$ret[$k] = $nv;
				}
			}
			if(count($ret)) {
				return $ret;
			}
			return NULL;
		} else {
			return $data;
		}
	}