@Override
    public String toString() {
        return "PutOutcome{" +
                "isSuccess=" + isSuccess +
                ", isDuplicate=" + isDuplicate +
                '}';
    }
@return An optional that states whether the entry put was a duplicate of
an existing key, if known.
stroom-lmdb/src/main/java/stroom/lmdb/PutOutcome.java