code: def nonzero_backward(inputs):
      """
      Args:
        inputs (list of nn.Variable): Incomming grads/inputs to/of the forward function.
        kwargs (dict of arguments): Dictionary of the corresponding function arguments.
  
      Return:
        list of Variable: Return the gradients wrt inputs of the corresponding function.
      """
      dy = inputs[0]
      x0 = inputs[1]
      raise NotImplementedError("nonzero_backward is not implemented.")
  
label_desc: Use image node_id 1 for calling a global function with example usage: nonzero_backward(inputs) without return types