Store <hexdata> in blockchain and return new txid.
        Utxos taken from <wifs> and change sent to <change_address>.
        <wifs>: '["privatekey_in_wif_format", ...]'

def store_nulldata(self, hexdata, wifs, change_address=None, txouts=None,
                       fee=10000, lock_time=0):
        """Store <hexdata> in blockchain and return new txid.
        Utxos taken from <wifs> and change sent to <change_address>.
        <wifs>: '["privatekey_in_wif_format", ...]'
        """
        rawtx = self.create_tx(txouts=txouts, lock_time=lock_time)
        rawtx = self.add_nulldata(rawtx, hexdata)
        rawtx = self.add_inputs(rawtx, wifs, change_address=change_address,
                                fee=fee)
        return self.publish(rawtx)