docs: public static Double getLearningRate(MultiLayerNetwork net, int layerNumber) {
          Layer l = net.getLayer(layerNumber).conf().getLayer();
          int iter = net.getIterationCount();
          int epoch = net.getEpochCount();
          if (l instanceof BaseLayer) {
              BaseLayer bl = (BaseLayer) l;
              IUpdater u = bl.getIUpdater();
              if (u != null && u.hasLearningRate()) {
                  double d = u.getLearningRate(iter, epoch);
                  if (Double.isNaN(d)) {
                      return null;
                  }
                  return d;
              }
              return null;
          }
          return null;
      }