public Optional<ValueStoreKey> get(final Txn<ByteBuffer> txn,
                                       final UID mapDefinitionUid,
                                       final long key) {
        return getAsBytes(txn, mapDefinitionUid, key)
                .map(valueSerde::deserialize);
    }
Looks up the supplied mapDefinitionUid and key in the store and attempts to find a range that includes the
passed key. It will scan backwards from key until it finds the first matching range. If no matching range
is found an empty Optional is returned.
stroom-pipeline/src/main/java/stroom/pipeline/refdata/store/offheapstore/databases/RangeStoreDb.java