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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_node(self, key):
 """ return the node with the key or None if it does not exist """

        self._check_if_open()
        try:
            if not key.startswith('/'):
                key = '/' + key
            return self._handle.get_node(self.root, key)
        except _table_mod.exceptions.NoSuchNodeError:
            return None