code: public INDArray output(INDArray input, boolean train, INDArray featuresMask, INDArray labelsMask) {
          return output(input, train, featuresMask, labelsMask, null);
      }
docs: Calculate the output of the network, with masking arrays. The masking arrays are used in situations such
  as one-to-many and many-to-one recurrent neural network (RNN) designs, as well as for supporting time series
  of varying lengths within the same minibatch.