code: public JsonObject exportForFts() {
          JsonObject result = JsonObject.create();
          for (MutationToken token : tokens) {
              String tokenKey = token.vbucketID() + "/" + token.vbucketUUID();
              Long seqno = result.getLong(tokenKey);
              if (seqno == null || seqno < token.sequenceNumber()) {
                  result.put(tokenKey, token.sequenceNumber());
              }
          }
          return result;
      }
docs: Exports the {@link MutationState} into a format recognized by the FTS search engine.
  
  @return the exported {@link JsonObject} for one FTS index.