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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_topological_order(self, cfg_node):
 """ Get the topological order of a CFG Node. :param cfg_node: A CFGNode instance. :return: An integer representing its order, or None if the CFGNode does not exist in the graph. """


        if not self._quasi_topological_order:
            self._quasi_topological_sort()

        return self._quasi_topological_order.get(cfg_node, None)