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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 query_parameters(self):
 """ A key to list of values mapping of the query parameters seen in the request. """

        result = getattr(self, "_query_parameters", None)
        if result is None:
            result = self._query_parameters = normalize_query_parameters(
                self.query_string)
        return result