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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 proxy_schema(self):
 """ Get the Proxy-Schema option of a request. :return: the Proxy-Schema values or None if not specified by the request :rtype : String """

        for option in self.options:
            if option.number == defines.OptionRegistry.PROXY_SCHEME.number:
                return option.value
        return None