Problem with imported Keras LSTM model

i have a question. I have a basic LSTM model with first layer being Masking layer. the input shape is (None, sequence length, feature length). I used KerasModelImport.importKerasSequentialModelAndWeights() to import the model, the model seems to be fine. Except when i create a sample input, it gives me nullpointer exception. Any idea why? I check the basicRNNExample case, seems like the input shape is like (None, feature length, sequence length). Does the importer take care of that?

Exception in thread "main" java.lang.NullPointerException
	at org.deeplearning4j.nn.layers.samediff.SameDiffLayer.activate(SameDiffLayer.java:125)
	at org.deeplearning4j.nn.layers.AbstractLayer.activate(AbstractLayer.java:257)
	at org.deeplearning4j.nn.layers.recurrent.MaskZeroLayer.activate(MaskZeroLayer.java:71)
	at org.deeplearning4j.nn.multilayer.MultiLayerNetwork.outputOfLayerDetached(MultiLayerNetwork.java:1301)
	at org.deeplearning4j.nn.multilayer.MultiLayerNetwork.output(MultiLayerNetwork.java:2419)
	at org.deeplearning4j.nn.multilayer.MultiLayerNetwork.output(MultiLayerNetwork.java:2382)
	at org.deeplearning4j.nn.multilayer.MultiLayerNetwork.output(MultiLayerNetwork.java:2373)
	at org.deeplearning4j.nn.multilayer.MultiLayerNetwork.output(MultiLayerNetwork.java:2360)
	at org.deeplearning4j.nn.multilayer.MultiLayerNetwork.predict(MultiLayerNetwork.java:2216)
	at DomainClassifier.main(DomainClassifier.java:58)

An you please also post the stack trace of the exception?