public Optional<ByteBuffer> getAsBytes(Txn<ByteBuffer> txn, final K key) {
        try (final PooledByteBuffer pooledKeyBuffer = getPooledKeyBuffer()) {
            final ByteBuffer keyBuffer = pooledKeyBuffer.getByteBuffer();
            serializeKey(keyBuffer, key);
            return getAsBytes(txn, keyBuffer);
        }
    }
Gets the de-serialised value (if found) for the passed key using a read txn.
This will fail if you are already inside a txn.
stroom-lmdb/src/main/java/stroom/lmdb/AbstractLmdbDb.java