Storm UI visualization throws NullPointerException

2020-03-09 19:59:01.756 o.a.s.d.u.r.StormApiResource qtp1919834117-167291 [ERROR] Failure getting topology visualization
java.lang.NullPointerException: null
        at org.apache.storm.stats.StatsUtil.mergeWithAddPair(StatsUtil.java:1855) ~[storm-server-2.2.0.y.jar:2.2.0.y]
        at org.apache.storm.stats.StatsUtil.expandAveragesSeq(StatsUtil.java:2308) ~[storm-server-2.2.0.y.jar:2.2.0.y]
        at org.apache.storm.stats.StatsUtil.aggregateAverages(StatsUtil.java:832) ~[storm-server-2.2.0.y.jar:2.2.0.y]
        at org.apache.storm.stats.StatsUtil.aggregateBoltStats(StatsUtil.java:731) ~[storm-server-2.2.0.y.jar:2.2.0.y]
        at org.apache.storm.stats.StatsUtil.boltStreamsStats(StatsUtil.java:900) ~[storm-server-2.2.0.y.jar:2.2.0.y]
        at org.apache.storm.daemon.ui.UIHelpers.getVisualizationData(UIHelpers.java:1939) ~[storm-webapp-2.2.0.y.jar:2.2.0.y]
        at org.apache.storm.daemon.ui.resources.StormApiResource.getTopologyVisualization(StormApiResource.java:423) ~[storm-webapp-2.2.0.y.jar:2.2.0.y]

for (K kk : mm1.keySet()) {
                    List seq1 = mm1.get(kk);
                    List seq2 = mm2.get(kk);
                    List sums = new ArrayList();
                    for (int i = 0; i < seq1.size(); i++) {
                        if (seq1.get(i) instanceof Long) {
                            sums.add(((Number) seq1.get(i)).longValue() + ((Number) seq2.get(i)).longValue());
                        } else {
                            sums.add(((Number) seq1.get(i)).doubleValue() + ((Number) seq2.get(i)).doubleValue());
                        }
                    }
                    tmp.put(kk, sums);
                }

public class  WordCountTopology extends ConfigurableTopology {
    private static final Logger LOG = LoggerFactory.getLogger(WordCountTopology.class);

    public static void main(String[] args) {
        ConfigurableTopology.start(new WordCountTopology(), args);
    }

    protected int run(String[] args) {
        TopologyBuilder builder = new TopologyBuilder();

        builder.setSpout("spout1", new RandomSpout(1), 1);
        builder.setSpout("spout2", new RandomSpout(2), 1);
        builder.setBolt("bolt", new RandomBolt(), 2).directGrouping("spout1", "stream1")
                .directGrouping("spout2", "stream2");

        String topologyName = "word-count";

        conf.setNumWorkers(3);

        if (args != null && args.length > 0) {
            topologyName = args[0];
        }
        return submit(topologyName, conf, builder);
    }

    static class RandomSpout extends BaseRichSpout {
        String stream;
        int id;

        public RandomSpout(int id) {
            this.id = id;
            stream = "stream" + id;
        }

        int taskId = 0;
        SpoutOutputCollector collector;
        public void open(Map<String, Object> conf, TopologyContext context, SpoutOutputCollector collector) {
            taskId = context.getThisTaskId();
            this.collector = collector;
        }

        /**
         * Different spout send tuples to different bolt via different stream.
         */
        public void nextTuple() {
            LOG.info("emitting {}", id);
            if (id == 1) {
                Values val = new Values("test a sentence");
                collector.emitDirect(2, stream, val, val);
            } else {
                Values val = new Values("test 2 sentence");
                collector.emitDirect(3, stream, val, val);
            }
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

        public void declareOutputFields(OutputFieldsDeclarer declarer) {
            declarer.declareStream(stream, new Fields("word"));
        }
    }

    static class RandomBolt extends BaseBasicBolt {

        public void execute(Tuple input, BasicOutputCollector collector) {
            LOG.info("executing:" + input.getSourceComponent());
        }

        public void declareOutputFields(OutputFieldsDeclarer declarer) {

        }
    }
}

                    List seq1 = mm1.get(kk);
                    List seq2 = mm2.get(kk);