docs: private Pair<Gradient, INDArray> getGradientsAndDelta(INDArray preOut, LayerWorkspaceMgr workspaceMgr) {
          // delta calculation
          ILossFunction lossFunction = layerConf().getLossFn();
          INDArray delta = lossFunction.computeGradient(getLabels2d(), preOut, layerConf().getActivationFn(), maskArray);
  
          // grab the empty gradient
          Gradient gradient = new DefaultGradient();
  
          delta = workspaceMgr.leverageTo(ArrayType.ACTIVATION_GRAD, delta);
          return new Pair<>(gradient, delta);
      }