#vulnerable code 
                                protected void calculate(ValuesProvider valuesProvider, List<ConnectionCandidate> connections, NeuralNetwork nn) {
	if (connections.size() > 0) {
	    List<Connections> chunk = new ArrayList<>();

	    for (int i = 0; i < connections.size(); i++) {
		ConnectionCandidate c = connections.get(i);
		chunk.add(c.connection);

		if (i == connections.size() - 1 || connections.get(i + 1).target != c.target) {
		    ConnectionCalculator cc = getConnectionCalculator(c.target);
		    if (cc != null) {
			Tensor t = TensorFactory.tensor(c.target, chunk, valuesProvider);
			t.forEach(j -> t.getElements()[j] = 0);
			cc.calculate(chunk, valuesProvider, c.target);
		    }

		    chunk.clear();

		    triggerEvent(new PropagationEvent(c.target, chunk, nn, valuesProvider));
		}
	    }
	}
    } 
                            #location 13 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                protected void calculate(ValuesProvider valuesProvider, List<ConnectionCandidate> connections, NeuralNetwork nn) {
	if (connections.size() > 0) {
	    List<Connections> chunk = new ArrayList<>();

	    for (int i = 0; i < connections.size(); i++) {
		ConnectionCandidate c = connections.get(i);
		chunk.add(c.connection);

		if (i == connections.size() - 1 || connections.get(i + 1).target != c.target) {
		    ConnectionCalculator cc = getConnectionCalculator(c.target);
		    if (cc != null) {
			Tensor t = TensorFactory.tensor(c.target, chunk, valuesProvider);
			float[] elements = t.getElements();
			IntStream.range(t.getStartIndex(), t.getStartIndex() + t.getSize()).forEach(j -> elements[j] = 0);
			cc.calculate(chunk, valuesProvider, c.target);
		    }

		    chunk.clear();

		    triggerEvent(new PropagationEvent(c.target, chunk, nn, valuesProvider));
		}
	    }
	}
    }