MnistMLPPreprocessed.java Exception in thread "main" java.lang.NullPointerException

gistfile1.txt

When I use MnistMLPPreprocessed.java to submit spark job. An ERROR find as below:
```
Exception in thread "main" java.lang.NullPointerException
        at org.deeplearning4j.spark.stats.StatsUtils.exportStatsAsHtml(StatsUtils.java:93)
        at org.deeplearning4j.spark.stats.StatsUtils.exportStatsAsHtml(StatsUtils.java:79)
        at org.deeplearning4j.spark.stats.StatsUtils.exportStatsAsHtml(StatsUtils.java:66)
        at org.deeplearning4j.mlp.MnistMLPPreprocessed.entryPoint(MnistMLPPreprocessed.java:150)
        at org.deeplearning4j.mlp.MnistMLPPreprocessed.main(MnistMLPPreprocessed.java:68)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.apache.spark.deploy.SparkSubmit$.org$apache$spark$deploy$SparkSubmit$$runMain(SparkSubmit.scala:731)
        at org.apache.spark.deploy.SparkSubmit$.doRunMain$1(SparkSubmit.scala:181)
        at org.apache.spark.deploy.SparkSubmit$.submit(SparkSubmit.scala:206)
        at org.apache.spark.deploy.SparkSubmit$.main(SparkSubmit.scala:121)
        at org.apache.spark.deploy.SparkSubmit.main(SparkSubmit.scala)
```
And I use myself path "hdfs:///user/yilaguan/SparkStats.html" in line 150 in MnistMLPPreprocessed.java:
```
StatsUtils.exportStatsAsHtml(stats, "hdfs:///user/yilaguan/SparkStats.html", sc);
```
I don't know how to solve it, Can you tell me?

gistfile2.txt

package org.deeplearning4j.mlp;

import com.beust.jcommander.JCommander;
import com.beust.jcommander.Parameter;
import com.beust.jcommander.ParameterException;
import org.apache.hadoop.io.BytesWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapred.SequenceFileOutputFormat;
import org.apache.spark.SparkConf;
import org.apache.spark.api.java.JavaPairRDD;
import org.apache.spark.api.java.JavaRDD;
import org.apache.spark.api.java.JavaSparkContext;
import org.deeplearning4j.datasets.iterator.impl.MnistDataSetIterator;
import org.deeplearning4j.mlp.sequence.FromSequenceFilePairFunction;
import org.deeplearning4j.mlp.sequence.ToSequenceFilePairFunction;
import org.deeplearning4j.nn.api.OptimizationAlgorithm;
import org.deeplearning4j.nn.conf.MultiLayerConfiguration;
import org.deeplearning4j.nn.conf.NeuralNetConfiguration;
import org.deeplearning4j.nn.conf.Updater;
import org.deeplearning4j.nn.conf.layers.DenseLayer;
import org.deeplearning4j.nn.conf.layers.OutputLayer;
import org.deeplearning4j.nn.weights.WeightInit;
import org.deeplearning4j.spark.api.Repartition;
import org.deeplearning4j.spark.api.RepartitionStrategy;
import org.deeplearning4j.spark.api.TrainingMaster;
import org.deeplearning4j.spark.api.stats.SparkTrainingStats;
import org.deeplearning4j.spark.data.DataSetExportFunction;
import org.deeplearning4j.spark.impl.multilayer.SparkDl4jMultiLayer;
import org.deeplearning4j.spark.impl.paramavg.ParameterAveragingTrainingMaster;
import org.deeplearning4j.spark.stats.StatsUtils;
import org.nd4j.linalg.dataset.DataSet;
import org.nd4j.linalg.dataset.api.iterator.DataSetIterator;
import org.nd4j.linalg.lossfunctions.LossFunctions;

import java.util.ArrayList;
import java.util.List;






/**
 * Train a MLP on MNIST data, using preprocessed DataSet objects (saved to a sequence file locally or on HDFS).
 *
 * Intended to be used locally. To use via Spark submit, set "-useSparkLocal false"
 *
 * @author Alex Black
 */
public class MnistMLPPreprocessed {

    @Parameter(names="-preprocessData", description = "Whether data should be saved and preprocessed (set to false to use already saved data)", arity = 1)
    private boolean preprocessData = true;

    @Parameter(names="-dataSavePath", description = "Directory in which to save the serialized data sets - required. For example, file:/C:/Temp/MnistMLPPreprocessed/", required = true)
    private String dataSavePath;

    @Parameter(names="-useSparkLocal", description = "Use spark local (helper for testing/running without spark submit)", arity = 1)
    private boolean useSparkLocal = false;

    @Parameter(names="-batchSizePerWorker", description = "Number of examples to fit each worker with")
    private int batchSizePerWorker = 32;

    @Parameter(names="-numEpochs", description = "Number of epochs for training")
    private int numEpochs = 3;

    public static void main(String[] args) throws Exception{
        new MnistMLPPreprocessed().entryPoint(args);
    }

    protected void entryPoint(String[] args) throws Exception {
        JCommander jcmdr = new JCommander(this);
        try{
            jcmdr.parse(args);
        } catch(ParameterException e){
            //User provides invalid input -> print the usage info
            jcmdr.usage();
            try{ Thread.sleep(500); } catch(Exception e2){ }
            throw e;
        }

        SparkConf sparkConf = new SparkConf();
        if(useSparkLocal) sparkConf.setMaster("local[*]");
        sparkConf.setAppName("MLP");
        sparkConf.set("spark.serializer", "org.apache.spark.serializer.KryoSerializer");
        sparkConf.set("spark.kryo.registrator", "org.nd4j.Nd4jRegistrator");
        JavaSparkContext sc = new JavaSparkContext(sparkConf);


        //First: preprocess data into a sequence file
        if(preprocessData) {
            DataSetIterator iter = new MnistDataSetIterator(batchSizePerWorker, true, 12345);
            List<DataSet> list = new ArrayList<>();
            while (iter.hasNext()) {
                list.add(iter.next());
            }

            JavaRDD<DataSet> rdd = sc.parallelize(list);
            JavaPairRDD<Text,BytesWritable> forSequenceFile = rdd.mapToPair(new ToSequenceFilePairFunction());
            forSequenceFile.saveAsHadoopFile(dataSavePath, Text.class, BytesWritable.class, SequenceFileOutputFormat.class);
        }

        //Second: load the data from a sequence file
        JavaPairRDD<Text,BytesWritable> sequenceFile = sc.sequenceFile(dataSavePath, Text.class, BytesWritable.class);
        JavaRDD<DataSet> trainData = sequenceFile.map(new FromSequenceFilePairFunction());


        //----------------------------------
        //Second: conduct network training

        //Network configuration:
        MultiLayerConfiguration conf = new NeuralNetConfiguration.Builder()
            .seed(12345)
            .optimizationAlgo(OptimizationAlgorithm.STOCHASTIC_GRADIENT_DESCENT)
            .iterations(1)
            .activation("relu")
            .weightInit(WeightInit.XAVIER)
            .learningRate(0.0069)
            .updater(Updater.NESTEROVS).momentum(0.9)
            .regularization(true).l2(1e-4)
            .list()
            .layer(0, new DenseLayer.Builder().nIn(28*28).nOut(500).build())
            .layer(1,  new DenseLayer.Builder().nIn(500).nOut(100).build())
            .layer(2, new OutputLayer.Builder(LossFunctions.LossFunction.NEGATIVELOGLIKELIHOOD)
                .activation("softmax").nIn(100).nOut(10).build())
            .pretrain(false).backprop(true)
            .build();

        //Configuration for Spark training: see http://deeplearning4j.org/spark for explanation of these configuration options
        TrainingMaster tm = new ParameterAveragingTrainingMaster.Builder(batchSizePerWorker)
            .averagingFrequency(10)
            .saveUpdater(true)
            .workerPrefetchNumBatches(2)
            .batchSizePerWorker(batchSizePerWorker)
            .repartionData(Repartition.Always)
            .repartitionStrategy(RepartitionStrategy.SparkDefault)
            .exportDirectory("hdfs:///user/yilaguan/deeplearning4jParmerter/")
            .build();

        SparkDl4jMultiLayer sparkNet = new SparkDl4jMultiLayer(sc, conf, tm);
//        sparkNet.setCollectTrainingStats(true);

        //Execute training:
        for( int i=0; i<numEpochs; i++ ){
            sparkNet.fit(trainData);
            System.out.println("Completed Epoch " + i);
        }

        SparkTrainingStats stats = sparkNet.getSparkTrainingStats();
        StatsUtils.exportStatsAsHtml(stats, "hdfs:///user/yilaguan/SparkStats.html", sc);

        System.out.println("----- DONE -----");
    }
}