ClassCastException while running TopWikipediaSessions

in the TopWikipediaSessions demo I saw this stack trace.

Stram event details
Stopped running due to an exception. java.lang.ClassCastException: org.apache.apex.malhar.lib.window.impl.InMemoryWindowedKeyedStorage cannot be cast to org.apache.apex.malhar.lib.window.SessionWindowedStorage
at org.apache.apex.malhar.lib.window.impl.KeyedWindowedOperatorImpl.assignSessionWindows(KeyedWindowedOperatorImpl.java:62)
at org.apache.apex.malhar.lib.window.impl.AbstractWindowedOperator.assignWindows(AbstractWindowedOperator.java:353)
at org.apache.apex.malhar.lib.window.impl.AbstractWindowedOperator.getWindowedValueWithTimestamp(AbstractWindowedOperator.java:317)
at org.apache.apex.malhar.lib.window.impl.AbstractWindowedOperator.processTuple(AbstractWindowedOperator.java:144)
at org.apache.apex.malhar.lib.window.impl.AbstractWindowedOperator$1.process(AbstractWindowedOperator.java:109)
at org.apache.apex.malhar.lib.window.impl.AbstractWindowedOperator$1.process(AbstractWindowedOperator.java:105)
at com.datatorrent.api.DefaultInputPort.put(DefaultInputPort.java:79)
at com.datatorrent.stram.stream.BufferServerSubscriber$BufferReservoir.sweep(BufferServerSubscriber.java:280)
at com.datatorrent.stram.engine.GenericNode.run(GenericNode.java:259)
at com.datatorrent.stram.engine.StreamingContainer$2.run(StreamingContainer.java:1415)