Why my all Gradients are zeros?

[kameronren]

I implement a ssd. It can run without Exception, but zhe gradients are allways zeros. below is my code. djl version is 0.11.0
`try (GradientCollector gc = Engine.getInstance().newGradientCollector()) {

				 NDList results = net.forward(parameterStore, X, true);
				 
				 if(firstTime == 0) {
					 
					 requiresGrad(net.getParameters());
				 }
				 
				 MultiBoxTarget mt = MultiBoxTarget.builder().build();
				 NDList inputs = new NDList(results.get(0));
				 inputs.add(Y.get(0));
				 inputs.add(results.get(1).transpose(0,2,1));
				 
				 NDList outputs =  mt.target(inputs);
				 
				 NDArray l = calc_loss(cls_loss,bbox_loss,new NDList(results.get(1)),new NDList(outputs.get(2)),new NDList(results.get(2)),new NDList(outputs.get(0)),new NDList(outputs.get(1)));
				 
				 
				 gc.backward(l);
				 
				 acc_sum += cls_eval(new NDList(results.get(1)),new NDList(outputs.get(2)));
				 n += outputs.get(2).size();
				 mae_sum += bbox_eval(new NDList(results.get(2)),new NDList(outputs.get(0)),new NDList(outputs.get(1)));
				 m += outputs.get(0).size();
				 
				 
			 }`

[RafaelaSeguro]

Hi, I know it has been a while since this question was asked, but I am having a similar problem, my gradients are all zero and I have tried debugging every part of my code and found nothing. Did you ever find an answer?