public Tuple2<Integer, Reply> mergedReply() {
        if (shouldReturnErrorReply()) {
            return createMergedErrorReplyResult();
        } else if (!successfullyMergedAtLeastOneReply()) {
            return createEmptyReplyResult();
        }
        return new Tuple2<>(successIndex, successReply);
    }
Encapsulated logic for merging replies from 1-n related DocumentProtocol messages.
For internal use only. Not multithread safe.
documentapi/src/main/java/com/yahoo/documentapi/messagebus/protocol/ReplyMerger.java