public function addUnconfirmedTxref($unconfirmedTxref)
    {
        if (!$this->getUnconfirmedTxrefs()) {
            return $this->setUnconfirmedTxrefs(array($unconfirmedTxref));
        } else {
            return $this->setUnconfirmedTxrefs(
                array_merge($this->getUnconfirmedTxrefs(), array($unconfirmedTxref))
            );
        }
    }