docs: public Map<String, INDArray> rnnGetPreviousState(int layer) {
          if (layer < 0 || layer >= layers.length)
              throw new IllegalArgumentException("Invalid layer number");
          Layer l = layers[layer];
          if(l instanceof org.deeplearning4j.nn.layers.wrapper.BaseWrapperLayer){
              l = ((org.deeplearning4j.nn.layers.wrapper.BaseWrapperLayer)l).getUnderlying();
          }
          if (!(l instanceof RecurrentLayer))
              throw new IllegalArgumentException("Layer is not an RNN layer");
          return ((RecurrentLayer) l).rnnGetPreviousState();
      }