public Txn<ByteBuffer> getTxn() {
            Objects.requireNonNull(writeTxn, "Transaction is closed");
            return writeTxn;
        }
@return The write txn object. Do NOT call close() on the returned txn,
use {@link WriteTxn#close()} or a try-with-resources block.
stroom-lmdb/src/main/java/stroom/lmdb/LmdbEnv.java