Map MXNet's sum operator attributes to onnx's ReduceSum operator
    and return the created node.

def convert_sum(node, **kwargs):
    """Map MXNet's sum operator attributes to onnx's ReduceSum operator
    and return the created node.
    """
    name, input_nodes, attrs = get_inputs(node, kwargs)

    mx_axis = attrs.get("axis", None)
    axes = convert_string_to_list(str(mx_axis)) if mx_axis is not None else None

    keepdims = get_boolean_attribute_value(attrs, "keepdims")

    if axes:
        node = onnx.helper.make_node(
            'ReduceSum',
            inputs=input_nodes,
            outputs=[name],
            axes=axes,
            keepdims=keepdims,
            name=name
        )
    else:
        node = onnx.helper.make_node(
            'ReduceSum',
            inputs=input_nodes,
            outputs=[name],
            keepdims=keepdims,
            name=name
        )
    return [node]