public Txn<ByteBuffer> getTxn() {
            checkState();
            if (writeTxn == null) {
                Objects.requireNonNull(writeTxnSupplier, "Has already been closed");
                writeTxn = writeTxnSupplier.get();
            }
            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