rem: transaction -> transaction_id = g_strdup (transaction_id);
add: if (transaction_id) transaction -> transaction_id = g_strdup (transaction_id); else transaction -> transaction_id = NULL;
context: gboolean gsb_data_transaction_set_transaction_id ( gint no_transaction,						   const gchar *transaction_id ){    struct_transaction *transaction;    transaction = gsb_data_transaction_get_transaction_by_no ( no_transaction);    if ( !transaction )	return FALSE;    transaction -> transaction_id = g_strdup (transaction_id);        return TRUE;}