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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 node_stat_delta(self, char, node, *, store=True):
 """Return a dictionary describing changes to a node's stats since the last time you looked at it. Deleted keys have the value ``None``. If the node's been deleted, this returns ``None``. """

        try:
            old = self._node_stat_cache[char].get(node, {})
            new = self.node_stat_copy(self._real.character[char].node[node])
            if store:
                self._node_stat_cache[char][node] = new
            r = dict_delta(old, new)
            return r
        except KeyError:
            return None