Error in GIS.trainModel

[Aditya Kulkarni]

Hello Everyone,

Piece of code:

SimpleEventStream eventStream = new SimpleEventStream();
                this.addEvents(   "male",   male, eventStream.getEvents() );
                this.addEvents( "female", female, eventStream.getEvents() );
                try {
                    return GIS.trainModel( (EventStream)eventStream, true);
                    //return GIS.trainModel( eventStream, 10, 0 );
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }

Error:
GIS.trainModel fails with following error:
==========================================================
Indexing events using cutoff of 0

    Computing event counts...  Exception in thread "main"
java.lang.NullPointerException
    at
opennlp.model.OnePassDataIndexer.computeEventCounts(OnePassDataIndexer.java:115)
    at opennlp.model.OnePassDataIndexer.<init>(OnePassDataIndexer.java:76)
    at opennlp.model.OnePassDataIndexer.<init>(OnePassDataIndexer.java:54)
    at opennlp.maxent.GISTrainer.trainModel(GISTrainer.java:240)
    at opennlp.maxent.GIS.trainModel(GIS.java:123)
    at opennlp.maxent.GIS.trainModel(GIS.java:76)
    at MaxentNameClassifier.train(MaxentNameClassifier.java:121)
    at MaxentNameClassifier.demo(MaxentNameClassifier.java:90)
    at MaxentNameClassifier.main(MaxentNameClassifier.java:62)
==========================================================

Please help! Also if there are any samples/tutorials for using this API,
that will be great pointer!

Thanks for your time.
-a